Liquid crystal diffraction element, optical element, image display unit, head-mounted display, beam steering, and sensor

ABSTRACT

Provided are a liquid crystal diffraction element having a high diffraction efficiency irrespective of diffraction angles, an optical element including the liquid crystal diffraction element, and an image display unit, a head-mounted display, a beam steering, and a sensor including the liquid crystal diffraction element or the optical element. The liquid crystal diffraction element includes: an optically-anisotropic layer that is formed of a liquid crystal composition including a liquid crystal compound, in which the optically-anisotropic layer has a liquid crystal alignment pattern in which a direction of an optical axis derived from the liquid crystal compound changes while continuously rotating in at least one in-plane direction, in a case where a length over which the direction of the optical axis derived from the liquid crystal compound rotates by 180° in a plane is set as a single period, a length of the single period in the liquid crystal alignment pattern gradually changes in the one in-plane direction, in a cross-sectional image of the optically-anisotropic layer obtained by observing a cross-section taken in a thickness direction parallel to the one in-plane direction with a scanning electron microscope, the optically-anisotropic layer has bright portions and dark portions extending from one surface to another surface and each of the dark portions has two or more inflection points of angle, the optically-anisotropic layer has regions where tilt directions of the dark portions are different from each other in the thickness direction, and an average tilt angle of the dark portion gradually changes in the one in-plane direction.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of PCT International Application No.PCT/JP2021/032176 filed on Sep. 1, 2021, which claims priority under 35U.S.C. § 119(a) to Japanese Patent Application No. 2020-147455 filed onSep. 2, 2020, Japanese Patent Application No. 2020-177293 filed on Oct.22, 2020, Japanese Patent Application No. 2021-035617 filed on Mar. 5,2021 and Japanese Patent Application No. 2021-065238 filed on Apr. 7,2021. The above applications are hereby expressly incorporated byreference, in its entirety, into the present application.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to a liquid crystal diffraction elementthat diffracts incidence light, an optical element including the liquidcrystal diffraction element, and an image display unit, a head-mounteddisplay, a beam steering, and a sensor including the liquid crystaldiffraction element or the optical element.

2. Description of the Related Art

An optical element that controls a direction of light is used in variousoptical devices or systems.

For example, the optical element that controls a direction of light isused in various optical devices that display a virtual image, variousinformation, or the like to be superimposed on a backlight unit of aliquid crystal display device and a scene that is actually being seen,for example, a head mounted display (HMD) such as Augmented Reality (AR)glasses, Virtual Reality (VR) glasses, or Mixed Reality (MR) glasses, aprojector, a head up display (HUD), a beam steering device, or a sensorfor detecting a thing or measuring the distance to a thing.

As the optical element that controls a direction light, a liquid crystaldiffraction element including an optically-anisotropic layer that isformed of a liquid crystal composition including a liquid crystalcompound is disclosed.

JP2010-525394A discloses a polarization diffraction grating including asubstrate and a first polarization diffraction grating layer on thesubstrate. The first polarization diffraction grating layer includes amolecular structure that is twisted according to a first twist senseover a first thickness defined between opposing faces of the firstpolarization diffraction grating layer. JP2010-525394A describes thatthe polarization diffraction grating layer can align liquid crystalmolecules in a predetermined alignment pattern to diffract light.

SUMMARY OF THE INVENTION

However, a liquid crystal diffraction element that changes a liquidcrystal alignment pattern in a plane to diffract light is expected to beapplied as an optical member for various optical devices. However, theliquid crystal diffraction element that changes a liquid crystalalignment pattern in a plane to diffract light has a problem in that, ina case where the diffraction angle increases, the diffraction efficiencydecreases, that is, the intensity of diffracted light decreases.

Therefore, in an element where the diffraction angle varies depending onlight incidence positions, for example, an element that exhibits a lensfunction by changing a liquid crystal alignment pattern in a plane todiffract light, there is a difference in diffraction efficiency betweenincidence positions in a plane of the element. That is, there is aproblem in that there is a region where the brightness of transmittedlight is low depending on incidence positions in a plane of the element.

An object of the present invention is to solve the above-describedproblem of the related art and to provide a liquid crystal diffractionelement having a high diffraction efficiency irrespective of diffractionangles, an optical element including the liquid crystal diffractionelement, and an image display unit, a head-mounted display, a beamsteering, and a sensor including the liquid crystal diffraction elementor the optical element.

In order to achieve the object, the present invention has the followingconfigurations.

[1] A liquid crystal diffraction element comprising:

an optically-anisotropic layer that is formed of a liquid crystalcomposition including a liquid crystal compound,

in which the optically-anisotropic layer has a liquid crystal alignmentpattern in which a direction of an optical axis derived from the liquidcrystal compound changes while continuously rotating in at least onein-plane direction,

in a case where a length over which the direction of the optical axisderived from the liquid crystal compound rotates by 180° in a plane isset as a single period, a length of the single period in the liquidcrystal alignment pattern gradually changes in the one in-planedirection,

in a cross-sectional image of the optically-anisotropic layer obtainedby observing a cross-section taken in a thickness direction parallel tothe one in-plane direction with a scanning electron microscope, theoptically-anisotropic layer has bright portions and dark portionsextending from one surface to another surface and each of the darkportions has two or more inflection points of angle,

the optically-anisotropic layer has regions where tilt directions of thedark portions are different from each other in the thickness direction,and

an average tilt angle of the dark portion gradually changes in the onein-plane direction.

[2] The liquid crystal diffraction element according to [1],

in which as the length of the single period in the liquid crystalalignment pattern decreases, the average tilt angle of the dark portionincreases.

[3] The liquid crystal diffraction element according to [1] or [2],

in which the number of inflection points where the tilt direction of thedark portion is folded is an odd number.

[4] The liquid crystal diffraction element according to any one of [1]to [3],

in which the number of inflection points where the tilt direction of thedark portion is folded is one.

[5] The liquid crystal diffraction element according to any one of [1]to [3],

in which the number of inflection points where the tilt direction of thedark portion is folded is three.

[6] The liquid crystal diffraction element according to any one of [1]to [5],

wherein the liquid crystal alignment pattern of theoptically-anisotropic layer is a concentric circular pattern having aconcentric circular shape where the one in-plane direction in which thedirection of the optical axis derived from the liquid crystal compoundchanges while continuously rotating moves from an inner side toward anouter side.

[7] The liquid crystal diffraction element according to [6],

in which in the optically-anisotropic layer, shapes of the brightportions and the dark portions in a cross-section of a center portion ofthe concentric circular shape are symmetrical with respect to a centerline of the optically-anisotropic layer in the thickness direction, andshapes of the bright portions and the dark portions in a cross-sectionof an end part of the concentric circular shape are asymmetrical withrespect to the center line of the optically-anisotropic layer in thethickness direction.

[8] The liquid crystal diffraction element according to [6],

in which in the optically-anisotropic layer, shapes of the brightportions and the dark portions in a cross-section of a center portion ofthe concentric circular shape are asymmetrical with respect to a centerline of the optically-anisotropic layer in the thickness direction, andshapes of the bright portions and the dark portions in a cross-sectionof an end part of the concentric circular shape are asymmetrical withrespect to the center line of the optically-anisotropic layer in thethickness direction.

[9] The liquid crystal diffraction element according to any one of [1]to [8],

in which a difference Δn₅₅₀ in refractive index generated by refractiveindex anisotropy of the optically-anisotropic layer is 0.2 or more.

[10] The liquid crystal diffraction element according to any one of [1]to [9],

in which a region where the length of the single period in the liquidcrystal alignment pattern is 1.0 μm or less is provided in a plane.

[11] An optical element comprising:

the liquid crystal diffraction element according to any one of [1] to[10]; and

a circularly polarizing plate.

[12] The optical element according to [11],

in which the circularly polarizing plate consists of a retardation plateand a polarizer, and

the liquid crystal diffraction element, the retardation plate, and thepolarizer are disposed in this order.

[13] The optical element according to [12],

in which the retardation plate is a λ/4 plate.

[14] The optical element according to [12] or [13],

in which the retardation plate has reverse wavelength dispersibility.

[15] An optical element comprising, in the following order:

the liquid crystal diffraction element according to any one of [1] to[10];

a silicon oxide layer; and

a support.

[16] An optical element comprising:

at least one liquid crystal diffraction element according to any one of[1] to [10] or at least one optical element according to any one of [11]to [15]; and

at least one phase modulation element.

[17] An image display unit comprising:

the liquid crystal diffraction element according to any one of [1] to[10] or the optical element according to any one of [11] to [15].

[18] A head-mounted display comprising:

the image display unit according to [17].

[19] Abeam steering comprising:

the liquid crystal diffraction element according to any one of [1] to[10] or the optical element according to any one of [11] to [15].

[20] A sensor comprising:

the liquid crystal diffraction element according to any one of [1] to[10] or the optical element according to any one of [11] to [15].

According to the present invention, the above-described problem of therelated art can be solved, and a liquid crystal diffraction elementhaving a high diffraction efficiency irrespective of diffraction anglescan be provided.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram conceptually showing one example of anoptically-anisotropic layer of a liquid crystal diffraction elementaccording to the present invention.

FIG. 2 is a plan view showing the optically-anisotropic layer shown inFIG. 1 .

FIG. 3 is an enlarged view showing a portion indicated by A in FIG. 1 .

FIG. 4 is an enlarged view showing a portion indicated by B in FIG. 1 .

FIG. 5 is a diagram conceptually showing another example of theoptically-anisotropic layer of the liquid crystal diffraction elementaccording to the present invention.

FIG. 6 is an enlarged view showing a portion indicated by C in FIG. 5 .

FIG. 7 is an enlarged view showing a portion indicated by D in FIG. 5 .

FIG. 8 is a partially enlarged view of a plan view of theoptically-anisotropic layer.

FIG. 9 is an enlarged cross-sectional view showing a partial region ofthe optically-anisotropic layer.

FIG. 10 is a diagram conceptually showing an example of an exposuredevice that exposes an alignment film.

FIG. 11 is a diagram conceptually showing an example of an exposuredevice that exposes an alignment film forming the optically-anisotropiclayer shown in FIG. 2 .

FIG. 12 is a conceptual diagram showing an action of theoptically-anisotropic layer.

FIG. 13 is a conceptual diagram showing the action of theoptically-anisotropic layer.

FIG. 14 is a conceptual diagram showing an action of the liquid crystaldiffraction element shown in FIG. 1 .

FIG. 15 is a diagram conceptually showing another example of theoptically-anisotropic layer.

FIG. 16 is a diagram conceptually showing another example of theoptically-anisotropic layer.

FIG. 17 is a diagram conceptually showing another example of theoptically-anisotropic layer.

FIG. 18 is a diagram conceptually showing another example of theoptically-anisotropic layer.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, a liquid crystal diffraction element, an optical element,an image display unit, a head-mounted display, a beam steering, and asensor according to the present invention will be described in detailbased on a preferable embodiment shown in the accompanying drawings.

In the present specification, numerical ranges represented by “to”include numerical values before and after “to” as lower limit values andupper limit values.

In the present specification, “(meth)acrylate” represents “either orboth of acrylate and methacrylate”.

In the present specification, visible light refers to light which can beobserved by human eyes among electromagnetic waves and refers to lightin a wavelength range of 380 to 780 nm. Invisible light refers to lightin a wavelength range of shorter than 380 nm or longer than 780 nm.

In the present specification, Re(λ) represents an in-plane retardationat a wavelength λ. Unless specified otherwise, the wavelength λ refersto 550 nm.

In the present specification, Re(λ) is a value measured at thewavelength λ using AxoScan (manufactured by Axometrics, Inc.). Byinputting an average refractive index ((nx+ny+nz)/3) and a filmthickness (d (μm)) to AxoScan, the following expressions can becalculated.

Slow Axis Direction (°)

Re(λ)=R0(λ)

R0(λ) is expressed as a numerical value calculated by AxoScan andrepresents Re(λ).

[Liquid Crystal Diffraction Element]

The liquid crystal diffraction element according to the embodiment ofthe present invention comprises:

an optically-anisotropic layer that is formed of a liquid crystalcomposition including a liquid crystal compound,

in which the optically-anisotropic layer has a liquid crystal alignmentpattern in which a direction of an optical axis derived from the liquidcrystal compound changes while continuously rotating in at least onein-plane direction,

in a case where a length over which the direction of the optical axisderived from the liquid crystal compound rotates by 180° in a plane isset as a single period, a length of the single period in the liquidcrystal alignment pattern gradually changes in the one in-planedirection,

in a cross-sectional image of the optically-anisotropic layer obtainedby observing a cross-section taken in a thickness direction parallel tothe one in-plane direction with a scanning electron microscope, theoptically-anisotropic layer has bright portions and dark portionsextending from one surface to another surface and each of the darkportions has two or more inflection points of angle,

the optically-anisotropic layer has regions where tilt directions of thedark portions are different from each other in the thickness direction,and

an average tilt angle of the dark portion gradually changes in the onein-plane direction.

FIG. 1 conceptually shows an example of the liquid crystal diffractionelement according to the present invention. FIG. 2 is a plan view in acase where the liquid crystal diffraction element (optically-anisotropiclayer) of FIG. 1 is seen from the top. FIG. 1 is a diagram conceptuallyshowing bright portions and dark portions observed due to a liquidcrystal phase in a case where an optically-anisotropic layer 36 a isobserved with a scanning electron microscope (SEM).

A liquid crystal diffraction element 10 a of FIGS. 1 and 2 includes theoptically-anisotropic layer 36 a that is formed of a compositionincluding a liquid crystal compound. The optically-anisotropic layer 36a is formed of a composition including a liquid crystal compound and hasa predetermined liquid crystal alignment pattern in which an opticalaxis derived from the liquid crystal compound changes while continuouslyrotating in at least one in-plane direction.

In the example shown in FIG. 2 , a liquid crystal alignment pattern in aliquid crystal layer 36 is a concentric circular pattern having aconcentric circular shape where the one in-plane direction (arrows A₁ toA₃) in which a direction of an optical axis of a liquid crystal compound40 changes while continuously rotating moves from an inner side towardan outer side. The concentric circular pattern is a pattern in which aline that connects liquid crystal compounds of which optical axes facethe same direction has a circular shape and circular line segments havea concentric circular shape. In other words, the liquid crystalalignment pattern of the optically-anisotropic layer 36 a shown in FIG.2 is a liquid crystal alignment pattern where the one in-plane directionin which the direction of the optical axis of the liquid crystalcompound 40 changes while continuously rotating is provided in a radialshape from the center of the liquid crystal layer 36.

In the optically-anisotropic layer 36 a shown in FIG. 2 , the opticalaxis (not shown) of the liquid crystal compound 40 is a longitudinaldirection of the liquid crystal compound 40.

In the optically-anisotropic layer 36 a, the direction of the opticalaxis of the liquid crystal compound 40 changes while continuouslyrotating in a direction in which a large number of optical axes move tothe outer side from the center of the optically-anisotropic layer 36 a,for example, a direction indicated by an arrow A₁, a direction indicatedby an arrow A₂, a direction indicated by an arrow A₃, or . . . . Thearrow A₁, the arrow A₂, and the arrow A₃ are arrangement axes describedbelow.

FIG. 1 is an image showing a cross-section taken along the arrow A₁observed with an SEM. SEM images showing a cross-section taken along thearrow A₂ and a cross-section taken along the A₃ are also as shown inFIG. 1 .

In addition, the optically-anisotropic layer 36 a in the liquid crystaldiffraction element 10 a has regions where the single periods Λ of theliquid crystal alignment pattern are different in a plane. Here, thesingle period Λ of the liquid crystal alignment pattern refers to alength (distance) over which the optical axis of the liquid crystalcompound 40 in the liquid crystal alignment pattern rotates by 180° inthe one in-plane direction in which the direction of the optical axischanges while continuously rotating.

Specifically, FIG. 1 is, for example, a diagram showing thecross-section taken along the arrow A₁ in FIG. 2 , and in the directionin which the direction of the optical axis derived from the liquidcrystal compound 40 changes while continuously rotating, the singleperiod Λ gradually decreases from the center toward the outer side. Thatis, in FIG. 1 , a single period Λ₂ in the vicinity of the outer side isshorter than a single period Λ₁ in the vicinity of the center portion.

In the present invention, the single period Λ gradually changingrepresents both of a case where the single period Λ continuously changesand a case where the single period Λ changes stepwise.

Although described below in detail, the diffraction angle of the liquidcrystal diffraction element depends on the single period Λ of the liquidcrystal alignment pattern, and as the single period Λ decreases, thediffraction angle increases.

In a case where the optically-anisotropic layer 36 a has theconfiguration in which the one in-plane direction in which the directionof the optical axis of the liquid crystal compound 40 in the liquidcrystal alignment pattern changes while continuously rotating isprovided in a radial shape from the center of the optically-anisotropiclayer 36 a and in which the single period Λ of the liquid crystalalignment pattern gradually decreases from the center toward the outerside in each of the one in-plane directions, circularly polarized lightincident into the optically-anisotropic layer 36 a having theabove-described liquid crystal alignment pattern is bent (diffracted)depending on individual local regions having different directions ofoptical axes of the liquid crystal compound 40. In this case, thediffraction angles vary depending on the single periods in the regionswhere circularly polarized light is incident. In theoptically-anisotropic layer 36 a having the concentric circular liquidcrystal alignment pattern, that is, the liquid crystal alignment patternin which the optical axis changes while continuously rotating in aradial shape, transmission of incidence light can be allowed asconverging light depending on the rotation direction of the optical axisof the liquid crystal compound 40 and the direction of circularlypolarized light to be incident.

That is, by setting the liquid crystal alignment pattern of theoptically-anisotropic layer 36 a in a concentric circular shape, theliquid crystal diffraction element 10 a exhibits, for example, afunction as a convex lens.

Here, in the present invention, as shown in FIG. 1 , in the SEM image ofthe optically-anisotropic layer 36 a, the optically-anisotropic layer 36a has the bright portions 42 and the dark portions 44 extending from onesurface to another surface, each of the dark portions 44 has two or moreinflection points of angle, the optically-anisotropic layer 36 a has theregions where the tilt directions of the dark portions 44 in thethickness direction are different from each other in the thicknessdirection, and an average tilt angle of the dark portion 44 graduallychanges in the one in-plane direction (arrows A₁, A₂, A₃, and the like)in which the direction of the optical axis of the liquid crystalcompound 40 changes while continuously changing.

In the example shown in FIG. 1 , the optically-anisotropic layer 36 ahas the stripe pattern of the bright portions 42 and the dark portions44, and the tilt angle of one dark portion 44 with respect to thesurface changes at two positions in the thickness direction. That is,each of the dark portions 44 has two inflection points. In addition, inall of the dark portions 44, a tilt direction in the upper region in thedrawing and a tilt direction in the lower region in the drawing areopposite to each other. That is, each of the dark portions 44 hasregions where the tilt directions are different. Specifically, in aportion of the optically-anisotropic layer 36 a shown in FIG. 1 on theright side from the center, the dark portion 44 is tilted in the rightdirection in an upper region in the drawing, and the dark portion 44 istilted in the left direction in a lower region in the drawing. On theother hand, in a portion of the optically-anisotropic layer 36 a shownin FIG. 1 on the left side from the center, the dark portion 44 istilted in the left direction in an upper region in the drawing, and thedark portion 44 is tilted in the right direction in a lower region inthe drawing.

In the present invention, in the optically-anisotropic layer 36 a, in acase where an angle between a line that connects a contact between eachof the dark portions 44 and one surface and a contact between the darkportion 44 and another surface and a line perpendicular to the mainsurface of the optically-anisotropic layer 36 a is represented by theaverage tilt angle, an average tilt angle of the dark portion 44gradually changes in the one in-plane direction (arrows A₁, A₂, A₃, andthe like) in which the direction of the optical axis of the liquidcrystal compound 40 changes while continuously changing. Specifically,in the example shown in FIG. 1 , the average tilt angle of the darkportion 44 in the vicinity of the center is about 0°, and the averagetilt angle gradually increases from the center toward an outer side.That is, in the optically-anisotropic layer 36 a in the example shown inthe drawing, as the single period Λ of the liquid crystal alignmentpattern gradually decreases, the average tilt angle of the dark portion44 gradually increases.

In the present invention, the average tilt angle of the dark portiongradually changing represents both of a case where the average tiltangle continuously changes and a case where the average tilt anglechanges stepwise.

It can also be said that the optically-anisotropic layer 36 a has threeregions (37 a, 37 b, 37 c) in the thickness direction, and the tiltangles of the dark portions 44 at the same position in the planedirection in the regions are different.

Here, the liquid crystal alignment of the optically-anisotropic layer 36a where the dark portion has two or more inflection points of angle andthe average tilt angle of the dark portion gradually changes will bedescribed using FIGS. 3 and 4 .

FIG. 3 is an enlarged conceptual diagram showing a portion indicated byA in FIG. 1 , and FIG. 4 is an enlarged conceptual diagram showing aportion indicated by B in FIG. 1 . That is, FIG. 3 is an enlargedconceptual diagram showing the center portion of theoptically-anisotropic layer 36 a, and FIG. 4 is an enlarged conceptualdiagram showing an outer side portion of the optically-anisotropic layer36 a. In addition, in FIGS. 3 and 4 , the arrangement of the liquidcrystal compounds 40 and the bright portions 42 and the dark portions 44observed with the SEM due to the liquid crystal phase are shown tooverlap each other. In FIG. 4 , only the liquid crystal compounds 40that face a direction parallel to the paper plane are shown. As in aportion surrounded by a broken line that is enlarged and shown in FIG. 4, the liquid crystal compounds 40 are arranged to rotatecounterclockwise to the right side in the drawing.

As shown in FIGS. 3 and 4 , in the optically-anisotropic layer 36 a, atany position in the thickness direction, the optical axis (now shown inthe drawing; the same direction as a longitudinal direction of theliquid crystal compound 40) derived from the liquid crystal compound 40rotates counterclockwise (to the left in a view from the upper side inthe drawing) from the center toward an outer side in the planedirection.

In addition, as shown in FIG. 3 , in the center portion, in the lowerregion 37 c in the thickness direction, the liquid crystal compound 40is aligned to be twisted clockwise (to the right) from the upper side tothe lower side in the drawing in the thickness direction.

On the other hand, in the middle region 37 b in the thickness direction,the liquid crystal compound 40 is not twisted in the thicknessdirection, and the optical axes of the liquid crystal compounds 40laminated in the thickness direction face the same direction. That is,it is preferable that the optical axes of the liquid crystal compounds40 present at the same position in the plane direction face the samedirection.

In addition, in the upper region 37 a in the thickness direction, theliquid crystal compound 40 is aligned to be twisted counterclockwise (tothe left) from the upper side to the lower side in the drawing in thethickness direction.

That is, in the region 37 a, the region 37 b, and the region 37 c of theoptically-anisotropic layer 36 a shown in FIG. 3 , the twisted states ofthe liquid crystal compounds 40 in the thickness direction are differentfrom each other.

The bright portions 42 and the dark portions 44 in the SEM image of theoptically-anisotropic layer 36 a are observed to connect the liquidcrystal compounds 40 facing the same direction. For example, in FIG. 3 ,the dark portions 44 are observed to connect the liquid crystalcompounds 40 of which the optical axes face a direction parallel to thepaper plane.

In the region 37 a, the region 37 b, and the region 37 c of theoptically-anisotropic layer 36 a shown in FIG. 3 , the twisted states ofthe liquid crystal compounds 40 in the thickness direction are differentfrom each other. Therefore, as shown in FIG. 3 , the bright portions 42and the dark portions 44 in the SEM image are formed in a substantiallyC-shape.

In addition, in the example shown in FIG. 3 , the thickness of theregion 37 a and the thickness of the region 37 c are substantially thesame, and the twisted angle of the thickness direction of the liquidcrystal compound 40 in the region 37 a and the twisted angle of thethickness direction of the liquid crystal compound 40 in the region 37 care substantially the same. Accordingly, in the dark portion 44 of theregion 37 a and the dark portion 44 of the region 37 c, the tiltdirections are opposite, and the tilt angles are the same. In the region37 b, the liquid crystal compounds 40 are not twisted in the thicknessdirection. Therefore, the dark portion 44 is not tilted. Accordingly,the average tilt angle of the dark portion 44 in the center portion ofthe optically-anisotropic layer 36 a is substantially 0°.

In addition, in the outer side portion shown in FIG. 4 , in the lowerregion 37 c in the thickness direction, the liquid crystal compound 40is aligned to be twisted clockwise (to the right) from the upper side tothe lower side in the drawing in the thickness direction. In the outerside portion of the region 37 c, the twisted angle of the thicknessdirection is larger than that of the center portion.

In addition, in the middle region 37 b in the thickness direction, theliquid crystal compound 40 is aligned to be twisted clockwise (to theright) from the upper side to the lower side in the drawing in thethickness direction.

In addition, the twisted angle of the thickness direction in the region37 c and the twisted angle of the thickness direction in the region 37 bare different. Accordingly, in the dark portion 44 of the region 37 cand the dark portion 44 of the region 37 b, the tilt directions are thesame, and the tilt angles are different.

On the other hand, in the upper region 37 a in the thickness direction,the liquid crystal compound 40 is aligned to be twisted counterclockwise(to the left) from the upper side to the lower side in the drawing inthe thickness direction. Accordingly, the tilt direction of the region37 a is opposite to that of the region 37 c and the region 37 b. Inaddition, in the outer side portion of the region 37 a, the twistedangle of the thickness direction is smaller than that of the centerportion. Therefore, the absolute value of the tilt angle of the darkportion 44 in the region 37 a is smaller than the absolute value of thetilt angle of the dark portion 44 in the region 37 c.

Accordingly, the average tilt angle of the dark portion 44 in the outerside portion of the optically-anisotropic layer 36 a is a value that isnot 0°.

In the example shown in FIG. 1 , in the region 37 a, the region 37 b,and the region 37 c of the optically-anisotropic layer 36 a, the singleperiod Λ of the liquid crystal alignment pattern gradually decreasesfrom the center toward the outer side. In addition, the right twist ofthe thickness direction in the region 37 c increases from the centertoward the outer side, the right twist of the thickness direction in theregion 37 b increases from the center toward the outer side, and theleft twist of the thickness direction in the region 37 a decreases fromthe center toward the outer side. As a result, it can be said that, ineach of the regions, the twist of the thickness direction at the centercan be imparted with the right twist toward the outer side.

By configuring the single periods Λ of the liquid crystal alignmentpatterns and the twisted angles of the thickness direction in the region37 a, the region 37 b, and the region 37 c as described above, theconfiguration in which the average tilt angle of the dark portion 44 issubstantially 0° in the center portion and gradually increases towardthe outer side can be adopted.

In the optically-anisotropic layer 36 a, as shown in FIG. 1 , it can besaid that shapes of the bright portions 42 and the dark portions 44 in across-section of a center portion of the concentric circular shape aresymmetrical with respect to a center line of the optically-anisotropiclayer 36 a in the thickness direction, and shapes of the bright portions42 and the dark portions 44 in a cross-section of an end part of theconcentric circular shape are asymmetrical with respect to the centerline of the optically-anisotropic layer 36 a in the thickness direction.

As described above, the liquid crystal diffraction element that changesa liquid crystal alignment pattern in a plane to diffract light has aproblem in that, in a case where the diffraction angle increases, thediffraction efficiency decreases, that is, the intensity of diffractedlight decreases. Specifically, in the diffraction of light by theoptically-anisotropic layer having the liquid crystal alignment patternin which the direction of the optical axis of the liquid crystalcompound changes while continuously rotating in a plane, there is aproblem in that, in a case where the diffraction angle increases, thediffraction efficiency decreases, that is, the intensity of diffractedlight decreases. Therefore, in a case where the optically-anisotropiclayer has regions having different lengths of the single periods overwhich the direction of the optical axis of the liquid crystal compoundrotates by 180° in a plane, the diffraction angle varies depending onlight incidence positions. Therefore, there is a difference in theamount of diffracted light depending on in-plane incidence positions.That is, there is a problem in that there is a region where thebrightness of transmitted and diffracted light is low depending onin-plane incidence positions.

On the other hand, in the liquid crystal diffraction element accordingto the embodiment of the present invention, in the configuration wherethe diffraction angle of light in a plane changes by gradually changingthe length of the single period in the liquid crystal alignment patternof the optically-anisotropic layer in the one in-plane direction, thedark portion observed in the SEM image of the optically-anisotropiclayer has two or more inflection points, the optically-anisotropic layerhas regions where tilt directions of the dark portions are differentfrom each other in the thickness direction, and the average tilt angleof the dark portion gradually changes in the direction in which thesingle period of the liquid crystal alignment pattern changes dependingon this change direction. By configuring the optically-anisotropic layeras described above, a decrease in diffraction efficiency can besuppressed even in the region where the diffraction angle is large. As aresult, the liquid crystal diffraction element where the diffractionefficiency is high irrespective of diffraction angles and the amount oftransmitted light is uniform can be obtained.

In addition, in the liquid crystal diffraction element according to theembodiment of the present invention, in the optically-anisotropic layer36 a, that is, the cross-sectional SEM image, the optically-anisotropiclayer 36 a has the bright portions 42 and the dark portions 44 extendingfrom one surface to another surface, each of the dark portions 44 hastwo or more inflection points of angle, and the optically-anisotropiclayer 36 a has the regions where the tilt directions are different inthe thickness direction. As a result, the wavelength dependence of thediffraction efficiency can be reduced, and light can be diffracted withthe same diffraction efficiency irrespective of wavelengths.

As described above, in the liquid crystal diffraction element includingthe optically-anisotropic layer having liquid crystal alignment patternin which the direction of the optical axis derived from the liquidcrystal compound continuously changes in at least one in-planedirection, incidence light in a wide wavelength range, for example, theentire wavelength range of visible light can be diffracted at differentdiffraction angles depending on the wavelengths.

However, according to the investigation by the present inventors, thecross-sectional SEM image of the liquid crystal diffraction elementhaving the liquid crystal alignment pattern in the related art has darkportions that are tilted with respect to the surface (main surface) butdoes not have the inflection point where the angle changes or has onlyone inflection point as described in JP2010-525394A. Therefore, in theliquid crystal diffraction element in the related art, the wavelengthdependence of the diffraction efficiency is large, for example, thediffraction efficiencies of red light and green light are high but thediffraction efficiency of blue light is lower than those of the othertwo colors.

On the other hand, in the liquid crystal diffraction element accordingto the embodiment of the present invention, the dark portion 44 observedin the cross-sectional SEM image has two or more inflection points ofangle and has the regions where the tilt directions are different in thethickness direction. As a result, the wavelength dependence of thediffraction efficiency can be reduced, and light can be diffracted withthe same diffraction efficiency irrespective of wavelengths. Further,light can be diffracted with high diffraction efficiency irrespective ofwavelengths.

Here, in the example shown in FIG. 1 , the optically-anisotropic layer36 a has two inflection points where the tilt angle of each of the darkportions 44 changes. However, the present invention is not limited tothis example, and each of the dark portions 44 may have three or moreinflection points.

In addition, in the example shown in FIG. 1 , in theoptically-anisotropic layer 36 a, each of the dark portions 44 otherthan the dark portion 44 positioned at the center in the left-rightdirection has one inflection point where the tilt direction is folded inthe opposite direction. Specifically, in each of the dark portions 44,the tilt direction in the region 37 a and the tilt direction in theregion 37 b are opposite to each other. Therefore, at the inflectionpoint positioned at the interface between the region 37 a and the region37 b, the tilt direction is folded in the opposite direction.

The present invention is not limited to the configuration where each ofthe dark portion 44 has one inflection point where the tilt direction isfolded in the opposite direction. Each of the dark portion 44 may havetwo or more inflection points where the tilt direction is folded in theopposite direction. It is preferable that the number of inflectionpoints where the tilt direction is folded in the opposite direction isan odd number.

FIG. 5 is a diagram conceptually showing another example of the liquidcrystal diffraction element according to the embodiment of the presentinvention. FIG. 5 is a diagram conceptually showing bright portions anddark portions observed due to a liquid crystal phase in a case where anoptically-anisotropic layer 36 b is observed with a scanning electronmicroscope (SEM).

In the example, the liquid crystal diffraction element 10 b shown inFIG. 5 includes the optically-anisotropic layer 36 b where the darkportion has three inflection points where the tilt direction is foldedin the opposite direction.

The liquid crystal diffraction element 10 b shown in FIG. 5 includes theoptically-anisotropic layer 36 b that is formed of a compositionincluding a liquid crystal compound. The optically-anisotropic layer 36b is formed of a composition including a liquid crystal compound and hasa predetermined liquid crystal alignment pattern in which an opticalaxis derived from the liquid crystal compound changes while continuouslyrotating in at least one in-plane direction. The plan view of theoptically-anisotropic layer 36 b is the same as FIG. 2 .

In addition, the optically-anisotropic layer 36 b in the liquid crystaldiffraction element 10 b has regions where the single periods Λ of theliquid crystal alignment pattern described below are different in aplane. That is, in FIG. 5 , a single period Λ₂ in the vicinity of theouter side is shorter than a single period Λ₁ in the vicinity of thecenter portion.

As in the optically-anisotropic layer 36 a, the optically-anisotropiclayer 36 b has the concentric circular liquid crystal alignment pattern,and the single period Λ of the liquid crystal alignment pattern changesfrom the center toward the outer side. Therefore, theoptically-anisotropic layer 36 b functions as a convex lens.

Here, as shown in FIG. 5 , in the SEM image of the optically-anisotropiclayer 36 b, the optically-anisotropic layer 36 b has the bright portions42 and the dark portions 44 extending from one surface to anothersurface, each of the dark portions 44 has three inflection points ofangle, the optically-anisotropic layer 36 b has the regions where thetilt directions of the dark portions 44 in the thickness direction aredifferent from each other in the thickness direction, and an averagetilt angle of the dark portion 44 gradually changes in the one in-planedirection in which the direction of the optical axis of the liquidcrystal compound 40 changes while continuously changing.

In the example shown in FIG. 5 , the optically-anisotropic layer 36 bhas the stripe pattern of the bright portions 42 and the dark portions44, and the tilt angle of each of the dark portions 44 with respect tothe surface changes at three positions in the thickness direction. Thatis, each of the dark portions 44 has three inflection points. Inaddition, in any dark portion 44, the tilt direction of the dark portion44 changes alternately in a region 37 d, a region 37 e, a region 37 f,and a region 37 g disposed from above in the drawing. That is, each ofthe dark portions 44 has regions where the tilt directions aredifferent. In addition, each of the dark portions 44 has threeinflection points where the tilt direction is folded in the oppositedirection.

Specifically, in a portion of the optically-anisotropic layer 36 b shownin FIG. 5 on the right side from the center, the dark portion 44 istilted in the right direction in the upper region 37 d in the drawing,the dark portion 44 is tilted in the left direction in the region 37 e,the dark portion 44 is tilted in the right direction in the region 37 f,and the dark portion 44 is tilted in the left direction in the region 37g. On the other hand, in a portion of the optically-anisotropic layer 36b on the left side from the center, the dark portion 44 is tilted in theleft direction in the upper region 37 d in the drawing, the dark portion44 is tilted in the right direction in the region 37 e, the dark portion44 is tilted in the left direction in the region 37 f, and the darkportion 44 is tilted in the right direction in the region 37 g.

In addition, in the optically-anisotropic layer 36 b, the average tiltangle of the dark portion 44 gradually changes in the one in-planedirection in which the direction of the optical axis of the liquidcrystal compound 40 changes while continuously changing. Specifically,in the example shown in FIG. 5 , the average tilt angle of the darkportion 44 in the vicinity of the center is about 0°, and the averagetilt angle gradually increases from the center toward an outer side.That is, in the optically-anisotropic layer 36 b in the example shown inthe drawing, as the single period Λ of the liquid crystal alignmentpattern gradually increases, the average tilt angle of the dark portion44 gradually increases.

It can also be said that the optically-anisotropic layer 36 b has fourregions (37 d, 37 e, 37 f, 37 g) in the thickness direction, and thetilt angles of the dark portions 44 at the same position in the planedirection in the regions are different.

The liquid crystal alignment of the optically-anisotropic layer 36 bwill be described using FIGS. 6 and 7 .

FIG. 6 is an enlarged conceptual diagram showing a portion indicated byC in FIG. 5 , and FIG. 7 is an enlarged conceptual diagram showing aportion indicated by D in FIG. 5 . That is, FIG. 6 is an enlargedconceptual diagram showing the center portion of theoptically-anisotropic layer 36 b, and FIG. 7 is an enlarged conceptualdiagram showing an outer side portion of the optically-anisotropic layer36 b. In addition, in FIGS. 6 and 7 , the arrangement of the liquidcrystal compounds 40 and the bright portions 42 and the dark portions 44observed with the SEM due to the liquid crystal phase are shown tooverlap each other. In FIG. 7 , only the liquid crystal compounds 40that face a direction parallel to the paper plane are shown. As in aportion surrounded by a broken line that is enlarged and shown in FIG. 7, the liquid crystal compounds 40 are arranged to rotatecounterclockwise to the right side in the drawing.

As shown in FIGS. 6 and 7 , in the optically-anisotropic layer 36 a, atany position in the thickness direction, the optical axis (now shown inthe drawing; the same direction as a longitudinal direction of theliquid crystal compound 40) derived from the liquid crystal compound 40rotates counterclockwise (to the left in a view from the upper side inthe drawing) from the center toward an outer side in the planedirection.

In addition, as shown in FIG. 6 , in the center portion, in the lowerregion 37 g in the thickness direction, the liquid crystal compound 40is aligned to be twisted clockwise (to the right) from the upper side tothe lower side in the drawing in the thickness direction.

On the other hand, in the upper region 37 f, the liquid crystal compound40 is aligned to be twisted counterclockwise (to the left) from theupper side to the lower side in the drawing in the thickness direction.

In addition, in the region 37 e, the liquid crystal compound 40 isaligned to be twisted clockwise (to the right) from the upper side tothe lower side in the drawing in the thickness direction.

In addition, in the upper region 37 d in the thickness direction, theliquid crystal compound 40 is aligned to be twisted counterclockwise (tothe left) from the upper side to the lower side in the drawing in thethickness direction.

That is, in the region 37 d to the region 37 g of theoptically-anisotropic layer 36 b shown in FIG. 6 , the twisted states ofthe liquid crystal compounds 40 in the thickness direction are differentfrom each other.

In the region 37 a, the region 37 b, and the region 37 c of theoptically-anisotropic layer 36 a shown in FIG. 3 , the twisted states ofthe liquid crystal compounds 40 in the thickness direction are differentfrom each other. Therefore, as shown in FIG. 6 , the bright portions 42and the dark portions 44 in the SEM image are formed in a substantiallyW-shape.

In addition, in the example shown in FIG. 6 , the thickness of theregion 37 d and the thickness of the region 37 g are substantially thesame, and the twisted angle of the thickness direction of the liquidcrystal compound 40 in the region 37 d and the twisted angle of thethickness direction of the liquid crystal compound 40 in the region 37 gare substantially the same. Accordingly, in the dark portion 44 of theregion 37 d and the dark portion 44 of the region 37 g, the tiltdirections are opposite, and the tilt angles are the same. In addition,the thickness of the region 37 e and the thickness of the region 37 fare substantially the same, and the twisted angle of the thicknessdirection of the liquid crystal compound 40 in the region 37 e and thetwisted angle of the thickness direction of the liquid crystal compound40 in the region 37 f are substantially the same. Accordingly, in thedark portion 44 of the region 37 e and the dark portion 44 of the region37 f, the tilt directions are opposite, and the tilt angles are thesame. Accordingly, the average tilt angle of the dark portion 44 in thecenter portion of the optically-anisotropic layer 36 b is substantially0°.

In addition, in the outer side portion shown in FIG. 7 , in the lowerregion 37 g in the thickness direction, the liquid crystal compound 40is aligned to be twisted clockwise (to the right) from the upper side tothe lower side in the drawing in the thickness direction. In the outerside portion of the region 37 g, the twisted angle of the thicknessdirection is larger than that of the center portion.

In addition, in the upper region 37 f, the liquid crystal compound 40 isaligned to be twisted counterclockwise (to the left) from the upper sideto the lower side in the drawing in the thickness direction. In theouter side portion of the region 37 f, the twisted angle of thethickness direction is larger than that of the center portion.

In addition, in the region 37 e, the liquid crystal compound 40 isaligned to be twisted clockwise (to the right) from the upper side tothe lower side in the drawing in the thickness direction. In the outerside portion of the region 37 e, the twisted angle of the thicknessdirection is larger than that of the center portion.

In addition, in the upper region 37 d, the liquid crystal compound 40 isaligned to be twisted counterclockwise (to the left) from the upper sideto the lower side in the drawing in the thickness direction. In theouter side portion of the region 37 d, the twisted angle of thethickness direction is smaller than that of the center portion.

Therefore, the tilt direction of the dark portion 44 in the region 37 gand the region 37 e and the tilt direction of the dark portion 44 in theregion 37 f and the region 37 d are different from each other. Inaddition, the absolute value of the tilt angle of the dark portion 44 inthe region 37 d is less than the absolute value of the tilt angle of thedark portion 44 in the other regions.

Accordingly, the average tilt angle of the dark portion 44 in the outerside portion of the optically-anisotropic layer 36 b is a value that isnot 0°.

By configuring the single periods Λ of the liquid crystal alignmentpatterns and the twisted angles of the thickness direction in the region37 d to the region 37 g as described above, the configuration in whichthe average tilt angle of the dark portion 44 is substantially 0° in thecenter portion and gradually increases toward the outer side can beadopted.

In the optically-anisotropic layer 36 b, as shown in FIG. 5 , it can besaid that shapes of the bright portions 42 and the dark portions 44 in across-section of a center portion of the concentric circular shape aresymmetrical with respect to a center line of the optically-anisotropiclayer 36 b in the thickness direction, and shapes of the bright portions42 and the dark portions 44 in a cross-section of an end part of theconcentric circular shape are asymmetrical with respect to the centerline of the optically-anisotropic layer 36 b in the thickness direction.

This way, even in a case where the optically-anisotropic layer 36 b hasthe configuration where the bright portions 42 and the dark portions 44are formed in a substantially W-shape and each of the dark portions 44has three inflection points where the tilt direction is folded in theopposite direction, in the configuration where the diffraction angle oflight varies in a plane, the liquid crystal diffraction element wherethe diffraction efficiency is high irrespective of diffraction anglesand the amount of transmitted light is uniform can be obtained.

In another example of the center portion, as conceptually shown in FIG.16 , the optically-anisotropic layer has four regions corresponding tothe inflection points of the dark portion 44 in the thickness direction.

In the example, in the lowermost region, the dark portion 44 is tiltedto the upper left side in the drawing. In the second region from below,the dark portion 44 is tilted to the upper left in the drawing at alarger angle than the lowermost region with respect to the surface. Inthe third region from below, the dark portion 44 is tilted to the upperright side in the drawing. Further, in the uppermost region, the darkportion 44 is tilted to the upper right in the drawing at a smallerangle than the third region from below with respect to the surface.

That is, the optically-anisotropic layer shown in FIG. 16 has threeinflection points of angle where the angle of the dark portion 44changes, and the inflection point where the tilt direction of the darkportion is folded is provided at one position at the interface betweenthe second region from below and the third region from below.

In the optically-anisotropic layer shown in FIG. 16 , the thicknesses inthe lowermost region and the uppermost region are the same, and thethicknesses in the second region from below and the third region frombelow are the same. Further, in the lowermost region and the uppermostregion, the tilt directions are different, but the angles (the absolutevalues of the angles) between the surface of the optically-anisotropiclayer and the dark portions 44 are the same. Likewise, in the secondregion from below and the third region from below, the tilt directionsare different, but the angles between the surface of theoptically-anisotropic layer and the dark portions 44 are the same.

That is, in the optically-anisotropic layer shown in FIG. 16 , thebright portions 42 and the dark portions 44 in the cross-sectional SEMimage are formed in a substantially C-shape. Accordingly, in theoptically-anisotropic layer shown in FIG. 16 , the shape of the darkportion 44 is symmetrical with respect to the center line in thethickness direction.

The angle of the dark portion 44 with respect to the surface of theoptically-anisotropic layer can be adjusted depending on the length ofthe single period over which the optical axis rotates by 180° in the onein-plane direction and the size of the twist of the liquid crystalcompound 40 that is twisted and aligned in the thickness directiondescribed below.

In another example of the center portion, as conceptually shown in FIG.17 , the optically-anisotropic layer has five regions corresponding tothe inflection points of the dark portion 44 in the thickness direction.

In the example, in the lowermost region, the dark portion 44 is tiltedto the upper left side in the drawing. In the second region from below,the dark portion 44 is tilted to the upper left in the drawing at alarger angle than the lowermost region with respect to the surface. Inthe third region from below, that is, the middle region in the thicknessdirection, the dark portion 44 extends in the thickness direction of theoptically-anisotropic layer. In the fourth region from below, the darkportion 44 is tilted to the upper right side in the drawing. Further, inthe uppermost region, the dark portion 44 is tilted to the upper rightin the drawing at a smaller angle than the fourth region from below withrespect to the surface.

That is, the optically-anisotropic layer shown in FIG. 17 has fourinflection points of angle where the angle of the dark portion 44changes.

In addition, the tilt directions of the dark portions 44 are opposite toeach other in the lowermost region and the second region from below, andare opposite to each other in the fourth region from below and theuppermost region. Therefore, at the inflection point positioned at theinterface between the second region from below and the fourth regionfrom below, the tilt direction is folded in the opposite direction. Thatis, the optically-anisotropic layer shown in FIG. 16 has one inflectionpoint where the tilt direction is folded in the opposite direction.

In the optically-anisotropic layer shown in FIG. 17 , the thicknesses inthe lowermost region and the uppermost region are the same, and thethicknesses in the second region from below and the second region fromabove are the same.

Further, in the lowermost region and the uppermost region of theoptically-anisotropic layer, the tilt directions are different, but theangles between the surface of the optically-anisotropic layer and thedark portions 44 are the same. Likewise, in the second region from belowand the fourth region from below, the tilt directions are different, butthe angles between the surface of the optically-anisotropic layer andthe dark portions 44 are the same. Further, in the third region frombelow that is positioned in the middle, the dark portion 44 extends inthe thickness direction of the optically-anisotropic layer.

That is, in the optically-anisotropic layer shown in FIG. 17 , thebright portions 42 and the dark portions 44 in the cross-sectional SEMimage are formed in a substantially C-shape. Accordingly, in theoptically-anisotropic layer shown in FIG. 4 , the shape of the darkportion 44 is symmetrical with respect to the center line in thethickness direction.

Further, in the optically-anisotropic layer of the liquid crystaldiffraction element according to the embodiment of the presentinvention, as in FIG. 18 conceptually showing the configurationincluding the substantially C-shaped dark portion 44 shown in FIGS. 16and 17 , a configuration in which the dark portion 44 continuouslychanges can also be adopted by reducing the interval between the regionsin the thickness direction, that is, the interval between the inflectionpoints in the thickness direction.

As described above, in the example of FIGS. 16 to 18 , the average tiltangle of the dark portion 44 in the outer side portion of theoptically-anisotropic layer is a value that is not 0°.

Accordingly, in the optically-anisotropic layer, it can be said thatshapes of the bright portions 42 and the dark portions 44 in across-section of a center portion of the concentric circular shape aresymmetrical with respect to a center line of the optically-anisotropiclayer in the thickness direction, and shapes of the bright portions 42and the dark portions 44 in a cross-section of an end part of theconcentric circular shape are asymmetrical with respect to the centerline of the optically-anisotropic layer in the thickness direction.

In the examples shown in FIGS. 1 to 5 and FIGS. 16 to 18 , shapes of thebright portions and the dark portions in a cross-section of a centerportion of the concentric circular shape are symmetrical with respect toa center line of the optically-anisotropic layer in the thicknessdirection, and shapes of the bright portions and the dark portions in across-section of an end part of the concentric circular shape areasymmetrical with respect to the center line of theoptically-anisotropic layer in the thickness direction. However, thepresent invention is not limited to this example, and shapes of thebright portions and the dark portions in a cross-section of a centerportion of the concentric circular shape may be asymmetrical withrespect to a center line of the optically-anisotropic layer in thethickness direction, and shapes of the bright portions and the darkportions in a cross-section of an end part of the concentric circularshape may be asymmetrical with respect to the center line of theoptically-anisotropic layer in the thickness direction.

In all of the above-described optically-anisotropic layers, the rod-likeliquid crystal compound is used as the liquid crystal compound. However,the present invention is not limited to this configuration, and adisk-like liquid crystal compound can also be used.

In the disk-like liquid crystal compound, the optical axis derived fromthe liquid crystal compound is defined as an axis perpendicular to adisk surface, that is so-called, a fast axis.

In addition, in the optically-anisotropic layer of the liquid crystaldiffraction element according to the embodiment of the presentinvention, as conceptually shown in FIG. 15 , the rod-like liquidcrystal compound and the disk-like liquid crystal compound may be usedin combination. By using the rod-like liquid crystal compound and thedisk-like liquid crystal compound in combination, light componentsincident at different angles can be diffracted with high diffractionefficiency. The combination of the rod-like liquid crystal compound andthe disk-like liquid crystal compound is not limited to theconfiguration conceptually shown in FIG. 15 , and various configurationscan be used. For example, in FIGS. 4, 6, 7, 16, 17, and 18 , therod-like liquid crystal compound and the disk-like liquid crystalcompound may be used in combination instead of using the rod-like liquidcrystal compound. In addition, for example, in FIG. 15 , and theabove-described combination, the rod-like liquid crystal compound andthe disk-like liquid crystal compound may be laminated in a moresegmented way in the thickness direction.

The liquid crystal diffraction elements 10 a and 10 b include only theoptically-anisotropic layer but may include other layers. For example,the liquid crystal diffraction element may include a support and analignment film during the formation of the optically-anisotropic layer.

Hereinafter, each of the components will be described.

FIG. 9 is an enlarged conceptual diagram showing the fine region of theliquid crystal diffraction element including the optically-anisotropiclayer 36 a (region 37 c). FIG. 8 is a front view showing theoptically-anisotropic layer 36 a shown in FIG. 9 .

The liquid crystal diffraction element in the example shown in FIG. 9includes a support 30, an alignment film 32, and theoptically-anisotropic layer 36 a.

<<Support>>

The support 30 supports the alignment film 32 and theoptically-anisotropic layer 36 a. As the support 30, varioussheet-shaped materials (films or plate-shaped materials) can be used aslong as they can support the alignment film and theoptically-anisotropic layer.

As the support 30, a transparent support is preferable, and examplesthereof include a polyacrylic resin film such as polymethylmethacrylate, a cellulose resin film such as cellulose triacetate, acycloolefin polymer film (for example, trade name “ARTON”, manufacturedby JSR Corporation; or trade name “ZEONOR”, manufactured by ZeonCorporation), polyethylene terephthalate (PET), polycarbonate, andpolyvinyl chloride. The support is not limited to a flexible film andmay be a non-flexible substrate such as a glass substrate.

In addition, the support 30 may have a multi-layer structure. Examplesof the multi-layer support include a support including: one of theabove-described supports having a single-layer structure that isprovided as a substrate; and another layer that is provided on a surfaceof the substrate.

The thickness of the support 30 is not particularly limited and may beappropriately set depending on the use of the liquid crystal diffractionelement, a material for forming the support 30, and the like in a rangewhere the alignment film and the optically-anisotropic layer can besupported.

The thickness of the support 30 is preferably 1 to 1000 μm, morepreferably 3 to 250 μm, and still more preferably 5 to 150 μm.

<<Alignment Film>>

The alignment film 32 is formed on the surface of the support 30.

The alignment film 32 is an alignment film for aligning the liquidcrystal compound 40 to the predetermined liquid crystal alignmentpattern during the formation of the optically-anisotropic layer 36 a.

As described above, in the liquid crystal diffraction element accordingto the embodiment of the present invention, the optically-anisotropiclayer has a liquid crystal alignment pattern in which a direction of anoptical axis 40A (refer to FIG. 8 ) derived from the liquid crystalcompound 40 changes while continuously rotating in one in-planedirection (arrow X direction described below). Accordingly, thealignment film is formed such that the optically-anisotropic layer canform the liquid crystal alignment pattern.

In addition, in the liquid crystal alignment pattern, a length overwhich the direction of the optical axis 40A rotates by 180° in the onein-plane direction in which the direction of the optical axis 40Achanges while continuously rotating is set as a single period Λ (arotation period of the optical axis).

In the following description, “the direction of the optical axis 40Arotates” will also be simply referred to as “the optical axis 40Arotates”.

As the alignment film, various well-known films can be used.

Examples of the alignment film include a rubbed film formed of anorganic compound such as a polymer, an obliquely deposited film formedof an inorganic compound, a film having a microgroove, and a film formedby lamination of Langmuir-Blodgett (LB) films formed with aLangmuir-Blodgett's method using an organic compound such asw-tricosanoic acid, dioctadecylmethylammonium chloride, or methylstearate.

The alignment film formed by a rubbing treatment can be formed byrubbing a surface of a polymer layer with paper or fabric in a givendirection multiple times. As the material used for the alignment film,for example, a material for forming polyimide, polyvinyl alcohol, apolymer having a polymerizable group described in JP1997-152509A(JP-H9-152509A), or an alignment film such as JP2005-97377A,JP2005-99228A, and JP2005-128503A is preferable.

In the liquid crystal diffraction element according to the embodiment ofthe present invention, for example, the alignment film can be suitablyused as a so-called photo-alignment film obtained by irradiating aphoto-alignment material with polarized light or non-polarized light.That is, in the liquid crystal diffraction element according to theembodiment of the present invention, a photo-alignment film that isformed by applying a photo-alignment material to the support 30 issuitably used as the alignment film.

The irradiation of polarized light can be performed in a directionperpendicular or oblique to the photo-alignment film, and theirradiation of non-polarized light can be performed in a directionoblique to the photo-alignment film.

Preferable examples of the photo-alignment material used in thephoto-alignment film that can be used in the present invention include:an azo compound described in JP2006-285197A, JP2007-76839A,JP2007-138138A, JP2007-94071A, JP2007-121721A, JP2007-140465A,JP2007-156439A, JP2007-133184A, JP2009-109831A, JP3883848B, andJP4151746B; an aromatic ester compound described in JP2002-229039A; amaleimide- and/or alkenyl-substituted nadiimide compound having aphoto-alignable unit described in JP2002-265541A and JP2002-317013A; aphotocrosslinking silane derivative described in JP4205195B andJP4205198B, a photocrosslinking polyimide, a photocrosslinkingpolyamide, or a photocrosslinking ester described in JP2003-520878A,JP2004-529220A, and JP4162850B; and a photodimerizable compound, inparticular, a cinnamate (cinnamic acid) compound, a chalcone compound,or a coumarin compound described in JP1997-118717A (JP-H9-118717A),JP1998-506420A (JP-H10-506420A), JP2003-505561A, WO2010/150748A,JP2013-177561A, and JP2014-12823A.

Among these, an azo compound, a photocrosslinking polyimide, aphotocrosslinking polyamide, a photocrosslinking ester, a cinnamatecompound, or a chalcone compound is suitably used.

The thickness of the alignment film is not particularly limited. Thethickness with which a required alignment function can be obtained maybe appropriately set depending on the material for forming the alignmentfilm.

The thickness of the alignment film is preferably 0.01 to 5 μm and morepreferably 0.05 to 2 μm.

A method of forming the alignment film is not limited. Any one ofvarious well-known methods corresponding to a material for forming thealignment film can be used. For example, a method including: applyingthe alignment film to a surface of the support 30; drying the appliedalignment film; and exposing the alignment film to laser light to forman alignment pattern can be used.

FIG. 10 conceptually shows an example of an exposure device that exposesthe alignment film to form an alignment pattern.

An exposure device 60 shown in FIG. 10 includes: a light source 64including a laser 62; an λ/2 plate 65 that changes a polarizationdirection of laser light M emitted from the laser 62; a beam splitter 68that splits the laser light M emitted from the laser 62 into two beamsMA and MB; mirrors 70A and 70B that are disposed on optical paths of thesplitted two beams MA and MB; and λ/4 plates 72A and 72B.

Although not shown in the drawing, the light source 64 emits linearlypolarized light P₀. The λ/4 plate 72A converts the linearly polarizedlight P₀ (beam MA) into right circularly polarized light P_(R), and theλ/4 plate 72B converts the linearly polarized light P₀ (beam MB) intoleft circularly polarized light P_(L).

The support 30 including the alignment film 32 on which the alignmentpattern is not yet formed is disposed at an exposed portion, the twobeams MA and MB intersect and interfere with each other on the alignmentfilm 32, and the alignment film 32 is irradiated with and exposed to theinterference light.

Due to the interference in this case, the polarization state of lightwith which the alignment film 32 is irradiated periodically changesaccording to interference fringes. As a result, in the alignment film32, an alignment pattern in which the alignment state periodicallychanges can be obtained. That is, an alignment film (hereinafter, alsoreferred to as “patterned alignment film”) having an alignment patternin which the alignment state changes periodically is obtained.

In the exposure device 60, by changing an intersecting angle α betweenthe two beams MA and MB, the period of the alignment pattern can beadjusted. That is, by adjusting the intersecting angle α in the exposuredevice 60, in the alignment pattern in which the optical axis 40Aderived from the liquid crystal compound 40 continuously rotates in theone in-plane direction, the length (single period Λ) of the singleperiod over which the optical axis 40A rotates by 180° in the onein-plane direction in which the optical axis 40A rotates can beadjusted.

By forming the optically-anisotropic layer on the patterned alignmentfilm having the alignment pattern in which the alignment stateperiodically changes, as described below, the optically-anisotropiclayer 36 a having the liquid crystal alignment pattern in which theoptical axis 40A derived from the liquid crystal compound 40continuously rotates in the one in-plane direction can be formed.

In addition, by rotating the optical axes of the λ/4 plates 72A and 72Bby 90°, respectively, the rotation direction of the optical axis 40A canbe reversed.

As described above, the patterned alignment film has an alignmentpattern to obtain the liquid crystal alignment pattern in which theliquid crystal compound is aligned such that the direction of theoptical axis of the liquid crystal compound in the optically-anisotropiclayer formed on the patterned alignment film changes while continuouslyrotating in at least one in-plane direction. In a case where an axis inthe direction in which the liquid crystal compound is aligned is analignment axis, it can be said that the patterned alignment film has analignment pattern in which the direction of the alignment axis changeswhile continuously rotating in at least one in-plane direction. Thealignment axis of the patterned alignment film can be detected bymeasuring absorption anisotropy. For example, in a case where the amountof light transmitted through the patterned alignment film is measured byirradiating the patterned alignment film with linearly polarized lightwhile rotating the patterned alignment film, it is observed that adirection in which the light amount is the maximum or the minimumgradually changes in the one in-plane direction.

In the liquid crystal diffraction element according to the embodiment ofthe present invention, the alignment film is provided as a preferableaspect and is not an essential component.

For example, the following configuration can also be adopted, in which,by forming the alignment pattern on the support 30 using a method ofrubbing the support 30, a method of processing the support 30 with laserlight or the like, or the like, the optically-anisotropic layer 36 a orthe like has the liquid crystal alignment pattern in which the directionof the optical axis 40A derived from the liquid crystal compound 40changes while continuously rotating in at least one in-plane direction.

The exposure device of the alignment film 32 is not limited to theexample shown in FIG. 10 . FIG. 11 shows another example of the exposuredevice that exposes the alignment film 32. The exposure device shown inFIG. 11 is used to form an alignment pattern having a concentriccircular shape on the alignment film as shown in FIG. 2 .

An exposure device 80 includes: a light source 84 that includes a laser82; a polarization beam splitter 86 that divides the laser light Memitted from the laser 82 into S polarized light MS and P polarizedlight MP; a mirror 90A that is disposed on an optical path of the Ppolarized light MP; a mirror 90B that is disposed on an optical path ofthe S polarized light MS; a lens 92 that is disposed on the optical pathof the S polarized light MS; a polarization beam splitter 94; and a λ/4plate 96.

The P polarized light MP that is split by the polarization beam splitter86 is reflected from the mirror 90A to be incident into the polarizationbeam splitter 94. On the other hand, the S polarized light MS that issplit by the polarization beam splitter 86 is reflected from the mirror90B and is collected by the lens 92 to be incident into the polarizationbeam splitter 94.

The P polarized light MP and the S polarized light MS are multiplexed bythe polarization beam splitter 94, are converted into right circularlypolarized light and left circularly polarized light by the λ/4 plate 96depending on the polarization direction, and are incident into thealignment film 32 on the support 30.

Here, due to interference between the right circularly polarized lightand the left circularly polarized light, the polarization state of lightwith which the alignment film is irradiated periodically changesaccording to interference fringes. The intersecting angle between theright circularly polarized light and the left circularly polarized lightchanges from the inside to the outside of the concentric circle.Therefore, an exposure pattern in which the pitch changes from the innerside to the outer side can be obtained. As a result, in the alignmentfilm, a concentric circular alignment pattern in which the alignmentstate periodically changes can be obtained.

In the exposure device 80, the single period Λ in the liquid crystalalignment pattern in which the optical axis of the liquid crystalcompound 40 continuously rotates by 180° in the one in-plane directioncan be controlled by changing the refractive power of the lens 92 (the Fnumber of the lens 92), the focal length of the lens 92, the distancebetween the lens 92 and the alignment film 32, and the like.

In addition, by adjusting the refractive power of the lens 92 (the Fnumber of the lens 92), the length Λ of the single period in the liquidcrystal alignment pattern in the one in-plane direction in which theoptical axis continuously rotates can be changed.

Specifically, In addition, the length Λ of the single period in theliquid crystal alignment pattern in the one in-plane direction in whichthe optical axis continuously rotates can be changed depending on alight spread angle at which light is spread by the lens 92 due tointerference with parallel light. More specifically, in a case where therefractive power of the lens 92 is weak, light is approximated toparallel light. Therefore, the length Λ of the single period in theliquid crystal alignment pattern gradually decreases from the inner sidetoward the outer side, and the F number increases. Conversely, in a casewhere the refractive power of the lens 92 becomes stronger, the length Λof the single period in the liquid crystal alignment pattern rapidlydecreases from the inner side toward the outer side, and the F numberdecreases.

Further, depending on the applications of the liquid crystal diffractionelement such as a case where it is desired to provide a light amountdistribution in transmitted light, a configuration in which regionshaving partially different lengths of the single periods Λ in thearrangement axis D direction are provided can also be used instead ofthe configuration in which the length of the single period Λ graduallychanges in the arrangement axis D direction. For example, as a method ofpartially changing the single period Λ, for example, a method ofscanning and exposing the photo-alignment film to be patterned whilefreely changing a polarization direction of laser light to be gatheredcan be used.

In addition, the wavelength of the laser light used for exposing thealignment film can be appropriately set depending on, for example, thekind of the alignment film to be used. For example, laser light havingin a wavelength range of deep ultraviolet light to visible light toinfrared light can be preferably used. For example, laser light having awavelength of 266 nm, 325 nm, 355 nm, 370 nm, 385 nm, 405 nm, or 460 nmcan be used, but the present invention is not limited to theabove-described example. Laser light having various wavelengths can beused depending on the kind of the alignment film and the like.

After providing the optically-anisotropic layer on the alignment film,the optically-anisotropic layer may be peeled or transferred from thealignment film. The transfer can also be performed multiple timesaccording to the bonding surface of the optically-anisotropic layer. Thepeeling or transfer method can be freely selected depending on thepurposes. For example, by temporarily transferring theoptically-anisotropic layer to a substrate including an adhesive layer,transferring the laminate to a thing as a transfer destination, andpeeling off the substrate, the interface of the optically-anisotropiclayer on the alignment film side can be caused to face the thing as thetransfer destination. In addition, in order to cause a surface of theoptically-anisotropic layer opposite to the alignment film to face thething side as the transfer destination, after bonding theoptically-anisotropic layer and the thing as the transfer destinationthrough an adhesive, the optically-anisotropic layer may be peeled offfrom the alignment film.

In a case where the optically-anisotropic layer is peeled off from thealignment film, in order to reduce damage (for example, fracture orcrack) to the optically-anisotropic layer and the alignment film, it ispreferable to adjust a peeling angle, a speed, or the like.

In addition, the alignment film may be repeatedly used in a range wherethere is no problem in aligning properties. Before providing theoptically-anisotropic layer on the alignment film, the alignment filmcan be cleaned with an organic solvent or the like.

<<Optically-Anisotropic Layer>>

The optically-anisotropic layer 36 a is formed on the surface of thealignment film 32.

In FIG. 8 , in order to simplify the drawing and to clarify theconfiguration of the optically-anisotropic layer 36 a, only the liquidcrystal compound 40 (liquid crystal compound molecules) on the surfaceof the alignment film in the first optically-anisotropic layer 36 a isshown. However, as conceptually shown in FIG. 9 showing theoptically-anisotropic layer 36 a, the optically-anisotropic layer 36 ahas a structure in which the aligned liquid crystal compounds 40 arelaminated as in an optically-anisotropic layer that is formed using acomposition including a typical liquid crystal compound.

As described above, in the liquid crystal diffraction element accordingto the embodiment of the present invention, the optically-anisotropiclayer 36 a is formed of the composition including the liquid crystalcompound.

In a case where an in-plane retardation value is set as λ/2, theoptically-anisotropic layer has a function of a general λ/2 plate, thatis, a function of imparting a phase difference of a half wavelength,that is, 180° to two linearly polarized light components in lightincident into the optically-anisotropic layer and are perpendicular toeach other.

Here, since the liquid crystal compound rotates to be aligned in a planedirection, the optically-anisotropic layer diffracts (refracts) incidentcircularly polarized light to be transmitted in a direction in which thedirection of the optical axis continuously rotates. At this time, thediffraction direction varies depending on the turning direction ofincident circularly polarized light.

That is, the optically-anisotropic layer allows transmission ofcircularly polarized light and diffracts this transmitted light.

In addition, the optically-anisotropic layer changes a turning directionof the transmitted circularly polarized light into an oppositedirection.

The optically-anisotropic layer has the liquid crystal alignment patternin which the direction of the optical axis derived from the liquidcrystal compound changes while continuously rotating in the one in-planedirection indicated by arrow D (hereinafter, also referred to as thearrangement axis D) in a plane of the optically-anisotropic layer. Inthe example shown in FIG. 8 , it is assumed that the direction of thearrangement axis D is the X direction and a direction perpendicular tothe direction of the arrangement axis D is the Y direction.

The optical axis 40A derived from the liquid crystal compound 40 is anaxis having the highest refractive index in the liquid crystal compound40, that is, a so-called slow axis. For example, in a case where theliquid crystal compound 40 is a rod-like liquid crystal compound, theoptical axis 40A is parallel to a rod-like major axis direction.

In the following description, the optical axis 40A derived from theliquid crystal compound 40 will also be referred to as “the optical axis40A of the liquid crystal compound 40” or “the optical axis 40A”.

In the optically-anisotropic layer, the liquid crystal compound 40 istwo-dimensionally aligned in a plane parallel to the arrow X directionand a Y direction perpendicular to the arrow X direction. In FIG. 1 ,FIGS. 3 and 4 , and FIGS. 5 to 7 , the Y direction is a directionperpendicular to the paper plane.

FIG. 8 conceptually shows a plan view of the optically-anisotropic layer36 a.

The plan view is a view in a case where the liquid crystal diffractionelement is seen from the top in FIG. 9 , that is, a view in a case wherethe liquid crystal diffraction element is seen from a thicknessdirection (laminating direction of the respective layers (films)). Inother words, the plan view is a view in a case where theoptically-anisotropic layer 36 a is seen from a direction perpendicularto the main surface.

In addition, in FIG. 8 , in order to clarify the configuration of theliquid crystal diffraction element according to the embodiment of thepresent invention, only the liquid crystal compound 40 on the surface ofthe alignment film 32 is shown. However, as described above, in thethickness direction, as shown in FIG. 9 , the optically-anisotropiclayer 36 a has the structure in which the liquid crystal compound 40 onthe surface of the alignment film 32 is laminated.

In FIG. 8 , a part in a plane of the optically-anisotropic layer 36 awill be described as a representative example. However, basically, theoptically-anisotropic layer also has the same configuration and the sameeffects as those of the optically-anisotropic layer 36 a, except thatthe lengths (single periods A) of the single periods of the liquidcrystal alignment patterns at in-plane positions of theoptically-anisotropic layer are different from each other.

The optically-anisotropic layer 36 a has the liquid crystal alignmentpattern in which the direction of the optical axis 40A derived from theliquid crystal compound 40 changes while continuously rotating in thearrangement axis D direction in a plane of the optically-anisotropiclayer 36 a.

Specifically, “the direction of the optical axis 40A of the liquidcrystal compound 40 changes while continuously rotating in thearrangement axis D direction (the predetermined one in-plane direction)”represents that an angle between the optical axis 40A of the liquidcrystal compound 40, which is arranged in the arrangement axis Ddirection, and the arrangement axis D direction varies depending onpositions in the arrangement axis D direction, and the angle between theoptical axis 40A and the arrangement axis D direction sequentiallychanges from θ to θ+180° or θ−180° in the arrangement axis D direction.

A difference between the angles of the optical axes 40A of the liquidcrystal compounds 40 adjacent to each other in the arrangement axis Ddirection is preferably 45° or less, more preferably 15° or less, andstill more preferably less than 15°.

On the other hand, regarding the liquid crystal compound 40 forming theoptically-anisotropic layer 36 a, the liquid crystal compounds 40 havingthe same direction of the optical axes 40A are arranged at regularintervals in the Y direction perpendicular to the arrangement axis Ddirection, that is, the Y direction perpendicular to the one in-planedirection in which the optical axis 40A continuously rotates.

In other words, regarding the liquid crystal compound 40 forming theoptically-anisotropic layer 36 a, in the liquid crystal compounds 40arranged in the Y direction, angles between the directions of theoptical axes 40A and the arrangement axis D direction are the same.

In the liquid crystal diffraction element according to the embodiment ofthe present invention, in the liquid crystal alignment pattern of theliquid crystal compound 40, the length (distance) over which thedirection of the optical axis 40A of the liquid crystal compound 40rotates by 180° in the arrangement axis D direction in which the opticalaxis 40A changes while continuously rotating in a plane is the length Λof the single period in the liquid crystal alignment pattern. In otherwords, the length of the single period in the liquid crystal alignmentpattern is defined as the distance between θ and θ+180° that is a rangeof the angle between the optical axis 40A of the liquid crystal compound40 and the arrangement axis D direction.

That is, a distance between centers of two liquid crystal compounds 40in the arrangement axis D direction is the length Λ of the singleperiod, the two liquid crystal compounds having the same angle in thearrangement axis D direction. Specifically, as shown in FIG. 8 , adistance between centers in the arrangement axis D direction of twoliquid crystal compounds 40 in which the arrangement axis D directionand the direction of the optical axis 40A match each other is the lengthΛ of the single period. In the following description, the length Λ ofthe single period will also be referred to as “single period Λ”.

In the liquid crystal diffraction element according to the embodiment ofthe present invention, in the liquid crystal alignment pattern of theoptically-anisotropic layer, the single period Λ is repeated in thearrangement axis D direction, that is, in the one in-plane direction inwhich the direction of the optical axis 40A changes while continuouslyrotating.

As described above, in the liquid crystal compounds arranged in the Ydirection in the optically-anisotropic layer, the angles between theoptical axes 40A and the arrangement axis D direction (the one in-planedirection in which the direction of the optical axis of the liquidcrystal compound 40 rotates) are the same. Regions where the liquidcrystal compounds 40 in which the angles between the optical axes 40Aand the arrangement axis D direction are the same are disposed in the Ydirection will be referred to as “regions R”.

In this case, it is preferable that an in-plane retardation (Re) valueof each of the regions R is a half wavelength, that is, λ/2. Thein-plane retardation is calculated from the product of a difference Δnin refractive index generated by refractive index anisotropy of theregion R and the thickness of the optically-anisotropic layer. Here, thedifference in refractive index generated by refractive index anisotropyof the region R in the optically-anisotropic layer is defined by adifference between a refractive index of a direction of an in-plane slowaxis of the region R and a refractive index of a direction perpendicularto the direction of the slow axis. That is, the difference Δn inrefractive index generated by refractive index anisotropy of the regionR is the same as a difference between a refractive index of the liquidcrystal compound 40 in the direction of the optical axis 40A and arefractive index of the liquid crystal compound 40 in a directionperpendicular to the optical axis 40A in a plane of the region R. Thatis, the difference Δn in refractive index is the same as the differencein refractive index of the liquid crystal compound.

In a case where circularly polarized light is incident into theabove-described optically-anisotropic layer 36 a, the light is refractedsuch that the direction of the circularly polarized light is converted.

This action is conceptually shown in FIG. 12 using theoptically-anisotropic layer 36 a. In FIG. 12 and FIG. 13 , in order tosimplify the drawing and to clarify the configuration of the liquidcrystal diffraction element, only the liquid crystal compound 40 (liquidcrystal compound molecules) on the surface of the alignment film in theoptically-anisotropic layer 36 a is shown.

In addition, in the optically-anisotropic layer 36 a, the value of theproduct of the difference in refractive index of the liquid crystalcompound and the thickness of the optically-anisotropic layer is λ/2.

As shown in FIG. 12 , in a case where the value of the product of thedifference in refractive index of the liquid crystal compound and thethickness of the optically-anisotropic layer in theoptically-anisotropic layer 36 a is λ/2 and incidence light L₁ as leftcircularly polarized light is incident into the optically-anisotropiclayer 36 a, the incidence light L₁ transmits through theoptically-anisotropic layer 36 a to be imparted with a retardation of180°, and the transmitted light L₂ is converted into right circularlypolarized light.

In addition, the liquid crystal alignment pattern formed in theoptically-anisotropic layer 36 a is a pattern that is periodic in thearrangement axis D direction. Therefore, the transmitted light L₂travels in a direction different from a traveling direction of theincidence light L₁. This way, the incidence light L₁ of the leftcircularly polarized light is converted into the transmitted light L₂ ofright circularly polarized light that is tilted by a predetermined anglein the arrangement axis D direction with respect to an incidencedirection.

On the other hand, as shown in FIG. 13 , in a case where the value ofthe product of the difference in refractive index of the liquid crystalcompound and the thickness of the optically-anisotropic layer in theoptically-anisotropic layer 36 a is λ/2 and incidence light L₄ as rightcircularly polarized light is incident into the optically-anisotropiclayer 36 a, the incidence light L₄ transmits through theoptically-anisotropic layer 36 a to be imparted with a retardation of180° and is converted into transmitted light L₅ of left circularlypolarized light.

In addition, the liquid crystal alignment pattern formed in theoptically-anisotropic layer 36 a is a pattern that is periodic in thearrangement axis D direction. Therefore, the transmitted light L₅travels in a direction different from a traveling direction of theincidence light L₄. In this case, the transmitted Light L₅ travels in adirection different from the transmitted light L₂, that is, in adirection opposite to the arrangement axis D direction with respect tothe incidence direction. This way, the incidence light L₄ is convertedinto the transmitted light L₅ of left circularly polarized light that istilted by a predetermined angle in a direction opposite to thearrangement axis D direction with respect to an incidence direction.

By changing the single period Λ of the liquid crystal alignment patternformed in the optically-anisotropic layer 36 a, refraction angles of thetransmitted light components L₂ and L₅ can be adjusted. Specifically,even in the optically-anisotropic layer 36 a, as the single period Λ ofthe liquid crystal alignment pattern decreases, light componentstransmitted through the liquid crystal compounds 40 adjacent to eachother more strongly interfere with each other. Therefore, thetransmitted light components L₂ and L₅ can be more largely refracted.

In addition, by reversing the rotation direction of the optical axis 40Aof the liquid crystal compound 40 that rotates in the arrangement axis Ddirection, the refraction direction of transmitted light can bereversed. That is, in the example FIGS. 12 and 13 , the rotationdirection of the optical axis 40A toward the arrangement axis Ddirection is clockwise. By setting this rotation direction to becounterclockwise, the refraction direction of transmitted light can bereversed.

Further, as described above, the optically-anisotropic layer 36 a hasregions in which the optical axis is twisted in a thickness direction ofthe optically-anisotropic layer and rotates, the regions havingdifferent twisted angles in the thickness direction and/or twisteddirections.

In the optically-anisotropic layer 36 a, it is preferable that thein-plane retardation value of the plurality of regions R is a halfwavelength. It is preferable that an in-plane retardationRe(550)=Δn₅₅₀×d of the plurality of regions R of theoptically-anisotropic layer 36 a with respect to the incidence lighthaving a wavelength of 550 nm is in a range defined by the followingExpression (1). Here, Δn₅₅₀ represents a difference in refractive indexgenerated by refractive index anisotropy of the region R in a case wherethe wavelength of incidence light is 550 nm, and d represents thethickness of the optically-anisotropic layer 36 a.

200 nm≤Δn ₅₅₀ ×d≤350 nm  (1).

That is, in a case where the in-plane retardation Re(550)=Δn₅₅₀×d of theplurality of regions R of the optically-anisotropic layer 36 a satisfiesExpression (1), a sufficient amount of a circularly polarized lightcomponent in light incident into the optically-anisotropic layer 36 acan be converted into circularly polarized light that travels in adirection tilted in a forward direction or reverse direction withrespect to the arrangement axis D direction. It is more preferable thatthe in-plane retardation Re(550)=Δn₅₅₀×d satisfies 225 nm≤Δn₅₅₀×d≤340nm, and it is still more preferable that the in-plane retardationRe(550)=Δn₅₅₀×d satisfies 250 nm≤Δn₅₅₀×d≤330 nm.

Expression (1) is a range with respect to incidence light having awavelength of 550 nm. However, an in-plane retardation Re(λ)=Δn_(λ)×d ofthe plurality of regions R of the optically-anisotropic layer withrespect to incidence light having a wavelength of λ nm is preferably ina range defined by the following Expression (1-2) and can beappropriately set.

0.7×(λ/2)nm≤Δn _(λ) ×d≤1.3×(λ/2)nm  (1-2)

In addition, the value of the in-plane retardation of the plurality ofregions R of the optically-anisotropic layer 36 a in a range outside therange of Expression (1) can also be used. Specifically, by satisfyingΔn₅₅₀×d<200 nm or 350 nm<Δn₅₅₀×d, the light can be classified into lightthat travels in the same direction as a traveling direction of theincidence light and light that travels in a direction different from atraveling direction of the incidence light. In a case where Δn₅₅₀×dapproaches 0 nm or 550 nm, the amount of the light component thattravels in the same direction as a traveling direction of the incidencelight increases, and the amount of the light component that travels in adirection different from a traveling direction of the incidence lightdecreases.

Further, it is preferable that an in-plane retardation Re(450)=Δn₄₅₀×dof each of the plurality of regions R of the optically-anisotropic layer36 a with respect to incidence light having a wavelength of 450 nm andan in-plane retardation Re(550)=Δn₅₅₀×d of each of the plurality ofregions R of the optically-anisotropic layer 36 a with respect toincidence light having a wavelength of 550 nm satisfy the followingExpression (2). Here, →n₄₅₀ represents a difference in refractive indexgenerated by refractive index anisotropy of the region R in a case wherethe wavelength of incidence light is 450 nm.

(Δn ₄₅₀ ×d)/(Δn ₅₅₀ ×d)<1.0  (2)

Expression (2) represents that the liquid crystal compound 40 in theoptically-anisotropic layer 36 a has reverse dispersibility. That is, bysatisfying Expression (2), the optically-anisotropic layer 36 a cancorrespond to incidence light having a wide range of wavelength.

The optically-anisotropic layer is formed of a cured layer of a liquidcrystal composition including a rod-like liquid crystal compound or adisk-like liquid crystal compound, and has a liquid crystal alignmentpattern in which an optical axis of the rod-like liquid crystal compoundor an optical axis of the disk-like liquid crystal compound is alignedas described above.

The optically-anisotropic layer is formed by forming the alignment filmhaving the above-described alignment pattern on the support and applyingthe liquid crystal composition to the alignment film, and curing theapplied liquid crystal composition. The structure of theoptically-anisotropic layer where the optical axis of the liquid crystalcompound is twisted in the thickness direction of theoptically-anisotropic layer and rotates can be formed by adding theabove-described chiral agent to the liquid crystal composition. Inaddition, the configuration where the twisted angle of the thicknessdirection varies depending on in-plane regions can be formed by adding aphotoreactive chiral agent to the liquid crystal composition, applyingthe liquid crystal composition to the alignment film, and irradiatingthe regions with light at different irradiation doses such that thehelical twisting power (HTP) of the photoreactive chiral agent variesdepending on the regions.

Specifically, the configuration of the optically-anisotropic layer wherethe twisted angle of the thickness direction varies depending onin-plane regions can be formed by using the chiral agent in which backisomerization, dimerization, isomerization, dimerization or the likeoccurs due to light irradiation such that the helical twisting power(HTP) changes and irradiating the liquid crystal composition for formingthe optically-anisotropic layer with light having a wavelength at whichthe HTP of the chiral agent changes before or during the curing of theliquid crystal composition while changing the irradiation dose dependingon the regions.

For example, by using a chiral agent in which the HTP decreases duringlight irradiation, the HTP of the chiral agent decreases during lightirradiation. Here, by changing the irradiation dose of light for each ofthe regions, for example, in a region that is irradiated with the lightat a high irradiation dose, the decrease in HTP is large, the inductionof helix is small, and thus the twisted angle of the twisted structuredecreases. On the other hand, in a region that is irradiated with thelight at a low irradiation dose, a decrease in HTP is small, and thusthe twisted angle of the twisted structure is large.

The method of changing the irradiation dose of light for each of theregions is not particularly limited, and a method of irradiating lightthrough a gradation mask, a method of changing the irradiation time foreach of the regions, or a method of changing the irradiation intensityfor each of the regions can be used.

The gradation mask refers to a mask in which a transmittance withrespect to light for irradiation changes in a plane.

Further in order to allow the optically-anisotropic layer to adopt theconfiguration where the dark portion has two or more inflection points,the optically-anisotropic layer has regions where tilt directions of thedark portions are different from each other in the thickness direction,and the average tilt angle of the dark portion gradually changes in thedirection in which the single period of the liquid crystal alignmentpattern changes depending on this change direction,optically-anisotropic layers having different configurations dependingon the regions in the thickness direction may be formed.

For example, in a case where the optically-anisotropic layer 36 a shownin FIG. 1 is formed, first, a liquid crystal composition including aphotoreactive chiral agent that induces right-twisting in the thicknessdirection is applied to the patterned alignment film that is formed onthe support, the regions are irradiated with light at differentirradiation doses such that the helical twisting power (HTP) of thephotoreactive chiral agent varies depending on the regions, and theliquid crystal composition is cured to form the region 37 c. Next, theliquid crystal composition including the photoreactive chiral agent isapplied to the formed region 37 c, the regions are irradiated with lightat different irradiation doses such that the HTP of the photoreactivechiral agent varies depending on the regions, and the liquid crystalcomposition is cured to form the region 37 b. In this case, in order toallow the region 37 b to have a structure different from that of theregion 37 c, the kind, content, or the like of each of the components inthe liquid crystal composition may be different from that of the region37 c, or the irradiation dose or the like of light for changing the HTPof the photoreactive chiral agent may be different from that of theregion 37 c. In addition, in a case where the liquid crystal compositionis applied to the region 37 c, the liquid crystal compounds 40 in theliquid crystal composition are arranged according to the arrangement ofthe liquid crystal compounds 40 present in the surface of the region 37c. Therefore, even in the region 37 b, the liquid crystal alignmentpattern where the single period Λ gradually changes in the arrangementaxis D direction is formed.

Further, the liquid crystal composition including the photoreactivechiral agent is applied to the formed region 37 b, the regions areirradiated with light at different irradiation doses such that the HTPof the photoreactive chiral agent varies depending on the regions, andthe liquid crystal composition is cured to form the region 37 a. In thiscase, the region 37 a is formed of a liquid crystal compositionincluding a photoreactive chiral agent that induces left-twisting in thethickness direction. In addition, in a case where the liquid crystalcomposition is applied to the region 37 b, the liquid crystal compounds40 in the liquid crystal composition are arranged according to thearrangement of the liquid crystal compounds 40 present in the surface ofthe region 37 b. Therefore, even in the region 37 a, the liquid crystalalignment pattern where the single period Λ gradually changes in thearrangement axis D direction is formed.

By forming the region 37 a, the region 37 b, and the region 37 c wherethe twisted states of the liquid crystal compounds 40 the thicknessdirection are different from each other as described above, theoptically-anisotropic layer having the configuration where each of thedark portions 44 has two or more inflection points of angle, theoptically-anisotropic layer has regions where tilt directions of thedark portions 44 are different from each other in the thicknessdirection, and the average tilt angle of the dark portion 44 graduallychanges in the one in-plane direction can be formed.

In addition, in the example shown in FIG. 3 , in theoptically-anisotropic layer according to the embodiment of the presentinvention, the optical axis derived from the liquid crystal compound isnot tilted with respect to the interface of the optically-anisotropiclayer. In the optically-anisotropic layer according to the embodiment ofthe present invention, the optical axis derived from the liquid crystalcompound may be tilted. For example, as described in WO2019/189586A, theoptical axis derived from the liquid crystal compound may have a pretiltangle with respect to the interface of the optically-anisotropic layer.In addition, as described in WO2020/122127A, the tilt angle of theoptical axis derived from the liquid crystal compound may change fromone interface to another interface of the optically-anisotropic layer inthe thickness direction. By tilting the optical axis derived from theliquid crystal compound with respect to the interface of theoptically-anisotropic layer, the retardation of theoptically-anisotropic layer can be appropriately adjusted to obtain ahigh diffraction efficiency.

In addition, in the optically-anisotropic layer according to theembodiment of the present invention, the film thickness of theoptically-anisotropic layer may change in a plane. The film thickness ofthe optically-anisotropic layer in a plane can be appropriately adjustedsuch that a high diffraction efficiency can be obtained with respect tolight components incident from different incidence positions.

In addition, as shown in the examples of FIGS. 3 and 4 , in each of theregion 37 a, the region 37 b, and the region 37 c of theoptically-anisotropic layer, the thicknesses of the center portion andthe outer side portion may be the same as or different from each other.The present invention is not limited to the above-described example, andin the liquid crystal diffraction element according to the embodiment ofthe present invention, the thickness of each of the regions of theoptically-anisotropic layer may be the same or change. The thickness ofeach of the regions of the optically-anisotropic layer may beappropriately set depending on the desired performance.

Although the optically-anisotropic layer functions as a so-called λ/2plate, the present invention also includes an aspect where a laminateincluding the support and the alignment film that are integratedfunctions as a so-called λ/2 plate.

In addition, the liquid crystal composition for forming theoptically-anisotropic layer includes a rod-like liquid crystal compoundor a disk-like liquid crystal compound and may further include othercomponents such as a leveling agent, an alignment control agent, apolymerization initiator, or an alignment assistant.

—Rod-Like Liquid Crystal Compound—

As the rod-like liquid crystal compound, an azomethine compound, anazoxy compound, a cyanobiphenyl compound, a cyanophenyl ester compound,a benzoate compound, a phenyl cyclohexanecarboxylate compound, acyanophenylcyclohexane compound, a cyano-substituted phenylpyrimidinecompound, an alkoxy-substituted phenylpyrimidine compound, aphenyldioxane compound, a tolan compound, or analkenylcyclohexylbenzonitrile compound is preferably used. As therod-like liquid crystal compound, not only the above-described lowmolecular weight liquid crystal molecules but also high molecular weightliquid crystal molecules can be used.

It is preferable that the alignment of the rod-like liquid crystalcompound is immobilized by polymerization. Examples of the polymerizablerod-like liquid crystal compound include compounds described inMakromol. Chem., (1989), Vol. 190, p. 2255, Advanced Materials (1993),Vol. 5, p. 107, U.S. Pat. Nos. 4,683,327A, 5,622,648A, 5,770,107A,WO95/22586A, WO95/24455A, WO97/00600A, WO98/23580A, WO98/52905A,JP1989-272551A (JP-H1-272551A), JP1994-16616A (JP-H6-16616A),JP1995-110469A (JP-H7-110469A), JP1999-80081A (JP-H11-80081A), andJP2001-64627. Further, as the rod-like liquid crystal compound, forexample, compounds described in JP1999-513019A (JP-H11-513019A) andJP2007-279688A can also be preferably used.

—Disk-Like Liquid Crystal Compound—

As the disk-like liquid crystal compound, for example, compoundsdescribed in JP2007-108732A and JP2010-244038A can be preferably used.

In a case where the disk-like liquid crystal compound is used in theoptically-anisotropic layer, the liquid crystal compound 40 rises in thethickness direction in the optically-anisotropic layer, and the opticalaxis 40A derived from the liquid crystal compound is defined as an axisperpendicular to a disk surface, that is so-called, a fast axis.

In order to obtain a high diffraction efficiency, it is preferable thata liquid crystal compound having high refractive index anisotropy Δn isused as the liquid crystal compound. By increasing the refractive indexanisotropy, a high diffraction efficiency can be maintained in a casewhere the incidence angle changes. The liquid crystal compound havinghigh refractive index anisotropy Δn is not particularly limited. Forexample, a compound described in WO2019/182129A or a compoundrepresented by Formula (I) can be preferably used.

In Formula (I),

P¹ and P² each independently represent a hydrogen atom, —CN, —NCS, or apolymerizable group.

Sp¹ and Sp² each independently represent a single bond or a divalentlinking group. Here, Sp¹ and Sp² do not represent a divalent linkinggroup including at least one group selected from the group consisting ofan aromatic hydrocarbon ring group, an aromatic heterocyclic group, andan aliphatic hydrocarbon ring group.

Z¹, Z², and Z³ each independently represents a single bond, —O—, —S—,—CHR—, —CHRCHR—, —OCHR—, —CHRO—, —SO—, —SO₂—, —COO—, —OCO—, —CO—S—,—S—CO—, —O—CO—O—, —CO—NR—, —NR—CO—, —SCHR—, —CHRS—, —SO—CHR—, —CHR—SO—,—SO₂—CHR—, —CHR—SO₂—, —CF₂O—, —OCF₂—, —CF₂S—, —SCF₂—, —OCHRCHRO—,—SCHRCHRS—, —SO—CHRCHR—SO—, —SO₂—CHRCHR—SO₂—, —CH═CH—COO—, —CH═CH—OCO—,—COO—CH═CH—, —OCO—CH═CH—, —COO—CHRCHR—, —OCO—CHRCHR—, —CHRCHR—COO—,—CHRCHR—OCO—, —COO—CHR—, —OCO—CHR—, —CHR—COO—, —CHR—OCO—, —CR═CR—,—CR═N—, —N═CR—, —N═N—, —CR═N—N═CR—, —CF═CF—, or —C≡C—. R represents ahydrogen atom or an alkyl group having 1 to 10 carbon atoms. In a casewhere a plurality of R's are present, R's may be the same as ordifferent from each other. In a case where a plurality of Z¹'s and aplurality of Z²'s are present, Z¹'s and Z²'s may be the same as ordifferent from each other. In a case where a plurality of Z³'s arepresent, Z³'s may be the same as or different from each other. Here, Z³connected to SP² represents a single bond.

X¹ and X² each independently represents a single bond or —S—. In a casewhere a plurality of X¹'s and a plurality of X²'s are present, X¹'s andX²'s may be the same as or different from each other. Here, among theplurality of X¹'s and a plurality of X²'s, at least one represents —S—.

k represents an integer of 2 to 4.

m and n each independently represent an integer of 0 to 3. In a casewhere a plurality of m's are present, m's may be the same as ordifferent from each other.

A¹, A², A³, and A⁴ each independently represent a group represented byany one of Formulas (B-1) to (B-7) or a group where two or three groupsamong the groups represented by Formulas (B-1) to (B-7) are linked. In acase where a plurality of A²'s and a plurality of A³'s are present, A²'sand A³'s may be the same as or different from each other. In a casewhere a plurality of A¹'s and a plurality of A⁴'s are present, A¹'s andA⁴'s may be the same as or different from each other.

In Formulas (B-1) to (B-7),

W¹ to W¹⁸ each independently represent CR¹ or N, and R¹ represents ahydrogen atom or the following substituent L.

Y¹ to Y⁶ each independently represent NR², O, or S, and R² represents ahydrogen atom or the following substituent L.

G¹ to G⁴ each independently represent CR³R⁴, NR⁵, O, or S, and R³ to R⁵each independently represent a hydrogen atom or the followingsubstituent L.

M¹ and M² each independently represent CR⁶ or N, and R⁶ represents ahydrogen atom or the following substituent L.

* represents a bonding position.

The substituent L represents an alkyl group having 1 to 10 carbon atoms,an alkoxy group having 1 to 10 carbon atoms, an alkylamino group having1 to 10 carbon atoms, an alkylthio group having 1 to 10 carbon atoms, analkanoyl group having 1 to 10 carbon atoms, an alkanoyloxy group having1 to 10 carbon atoms, an alkanoylamino group having 1 to 10 carbonatoms, an alkanoylthio group having 1 to 10 carbon atoms, analkyloxycarbonyl group having 2 to 10 carbon atoms, analkylaminocarbonyl group having 2 to 10 carbon atoms, analkylthiocarbonyl group having 2 to 10 carbon atoms, a hydroxy group, anamino group, a mercapto group, a carboxy group, a sulfo group, an amidegroup, a cyano group, a nitro group, a halogen atom, or a polymerizablegroup. Here, in a case where the group described as the substituent Lhas —CH₂—, a group in which at least one —CH₂— in the group issubstituted with —O—, —CO—, —CH═CH—, or —C≡C— is also included in thesubstituent L. Here, in a case where the group described as thesubstituent L has a hydrogen atom, a group in which at least onehydrogen atom—in the group is substituted with at least one selectedfrom the group consisting of a fluorine atom and a polymerizable groupis also included in the substituent L.

In order to maintain a high diffraction efficiency in a case where theincidence angle changes, the refractive index anisotropy Δn₅₅₀ of theliquid crystal compound is preferably 0.15 or more, more preferably 0.2or more, still more preferably 0.25 or more, and most preferably 0.3 ormore.

In addition, in the liquid crystal diffraction element according to theembodiment of the present invention, the refractive index anisotropy Δnor the average refractive index of the optically-anisotropic layer maychange in a plane. By changing the refractive index anisotropy Δn or theaverage refractive index of the optically-anisotropic layer in a plane,the diffraction efficiency can be appropriately adjusted with respect tolight components incident from different incidence positions.

—Photoreactive Chiral Agent—

The photoreactive chiral agent is formed of, for example, a compoundrepresented by the following Formula (I) and has properties capable ofcontrolling an aligned structure of the liquid crystal compound andchanging a helical pitch of the liquid crystal compound, that is, ahelical twisting power (HTP) of a helical structure during lightirradiation. That is, the photoreactive chiral agent is a compound thatcauses a helical twisting power of a helical structure derived from aliquid crystal compound, preferably, a nematic liquid crystal compoundto change during light irradiation (ultraviolet light to visible lightto infrared light), and includes a portion including a chiral portionand a portion in which a structural change occurs during lightirradiation as necessary portions (molecular structural units). However,the photoreactive chiral agent represented by the following Formula (I)can significantly change the HTP of liquid crystal molecules.

The above-described HTP represents the helical twisting power of ahelical structure of liquid crystal, that is, HTP=1/(Pitch×Chiral AgentConcentration [Mass Fraction]). For example, the HTP can be obtained bymeasuring a helical pitch (single period of the helical structure; μm)of a liquid crystal molecule at a given temperature and converting themeasured value into a value [μm⁻¹] in terms of the concentration of thechiral agent. In a case where a selective reflection color is formed bythe photoreactive chiral agent depending on the illuminance of light, achange ratio in HTP (HTP before irradiation/HTP after irradiation) ispreferably 1.5 or higher and more preferably 2.5 or higher in a casewhere the HTP decreases after irradiation, and is preferably 0.7 orlower and more preferably 0.4 or lower in a case where the HTP increasesafter irradiation.

Next, the compound represented by Formula (I) will be described.

In the formula, R represents a hydrogen atom, an alkoxy group having 1to 15 carbon atoms, an acryloyloxyalkyloxy group having 3 to 15 carbonatoms in total, or a methacryloyloxyalkyloxy group having 4 to 15 carbonatoms in total.

Examples of the alkoxy group having 1 to 15 carbon atoms include amethoxy group, an ethoxy group, a propoxy group, a butoxy group, ahexyloxy group, and a dodecyloxy group. In particular, an alkoxy grouphaving 1 to 12 carbon atoms is preferable, and an alkoxy group having 1to 8 carbon atoms is more preferable.

Examples of the acryloyloxyalkyloxy group having 3 to 15 carbon atoms intotal include an acryloyloxyethyloxy group, an acryloyloxybutyloxygroup, and an acryloyloxydecyloxy group. In particular, anacryloyloxyalkyloxy group having 5 to 13 carbon atoms is preferable, andan acryloyloxyalkyloxy group having 5 to 11 carbon atoms is morepreferable.

Examples of the methacryloyloxyalkyloxy group having 4 to 15 carbonatoms in total include a methacryloyloxyethyloxy group, amethacryloyloxybutyloxy group, and a methacryloyloxydecyloxy group. Inparticular, a methacryloyloxyalkyloxy group having 6 to 14 carbon atomsis preferable, and a methacryloyloxyalkyloxy group having 6 to 12 carbonatoms is more preferable.

The molecular weight of the photoreactive chiral agent represented byFormula (I) is preferably 300 or higher. In addition, it is preferablethat the solubility in the liquid crystal compound described below ishigh, and it is more preferable that the solubility parameter SP valueis close to that of the liquid crystal compound.

Hereinafter, specific examples (exemplary compounds (1) to (15)) of thecompound represented by Formula (I) will be shown, but the presentinvention is not limited thereto.

In the present invention, as the photoreactive chiral agent, forexample, a photoreactive optically active compound represented by thefollowing Formula (II) is also used.

In the formula, R represents a hydrogen atom, an alkoxy group having 1to 15 carbon atoms, an acryloyloxyalkyloxy group having 3 to 15 carbonatoms in total, or a methacryloyloxyalkyloxy group having 4 to 15 carbonatoms in total.

Examples of the alkoxy group having 1 to 15 carbon atoms include amethoxy group, an ethoxy group, a propoxy group, a butoxy group, ahexyloxy group, an octyloxy group, and a dodecyloxy group. Inparticular, an alkoxy group having 1 to 10 carbon atoms is preferable,and an alkoxy group having 1 to 8 carbon atoms is more preferable.

Examples of the acryloyloxyalkyloxy group having 3 to 15 carbon atoms intotal include an acryloyloxy group, an acryloyloxyethyloxy group, anacryloyloxypropyloxy group, an acryloyloxyhexyloxy group, anacryloyloxybutyloxy group, and an acryloyloxydecyloxy group. Inparticular, an acryloyloxyalkyloxy group having 3 to 13 carbon atoms ispreferable, and an acryloyloxyalkyloxy group having 3 to 11 carbon atomsis more preferable.

Examples of the methacryloyloxyalkyloxy group having 4 to 15 carbonatoms in total include a methacryloyloxy group, amethacryloyloxyethyloxy group, and a methacryloyloxyhexyloxy group. Inparticular, a methacryloyloxyalkyloxy group having 4 to 14 carbon atomsis preferable, and a methacryloyloxyalkyloxy group having 4 to 12 carbonatoms is more preferable.

The molecular weight of the photoreactive optically active compoundrepresented by Formula (II) is preferably 300 or higher. In addition, itis preferable that the solubility in the liquid crystal compounddescribed below is high, and it is more preferable that the solubilityparameter SP value is close to that of the liquid crystal compound.

Hereinafter, specific examples (exemplary compounds (21) to (32)) of thephotoreactive optically active compound represented by Formula (II) willbe shown, but the present invention is not limited thereto.

In addition, the photoreactive chiral agent can also be used incombination with a chiral agent having no photoreactivity such as achiral compound having a large temperature dependence of the helicaltwisting power. Examples of the well-known chiral agent having nophotoreactivity include chiral agents described in JP2000-44451A,JP1998-509726A (JP-H10-509726A), WO1998/00428A, JP2000-506873A,JP1997-506088A (JP-H9-506088A), Liquid Crystals (1996, 21, 327), andLiquid Crystals (1998, 24, 219).

<Action of Liquid Crystal Diffraction Element>

As described above, the optically-anisotropic layer that is formed usingthe composition including the liquid crystal compound and has the liquidcrystal alignment pattern in which the direction of the optical axis 40Arotates in the arrangement axis D direction refracts circularlypolarized light, in which as the single periods Λ of the liquid crystalalignment pattern decreases, the refraction angle is large.

Therefore, as in the example shown in FIG. 1 , in a case where theoptically-anisotropic layer that has a concentric circular shape wherethe one in-plane direction (arrangement axis D direction) in which thedirection of the optical axis derived the liquid crystal compoundchanges while continuously rotating moves from an inner side toward anouter side and where the single period Λ decreases from the centertoward an outer side is formed, as shown in FIG. 14 , light L₆ incidentinto the vicinity of the center in a plane of the optically-anisotropiclayer 36 a transmits through the optically-anisotropic layer 36 a aslight L₇ without being substantially diffracted. In addition, light L₈incident into a middle region between the center and an outer region onthe right side in the drawing is diffracted to the center side andtransmits through the optically-anisotropic layer 36 a as light L₉. Inaddition, light L₁₀ incident into the outer region on the right side inthe drawing is diffracted to the center side at a larger angle andtransmits through the optically-anisotropic layer 36 a as light L₁₁. Inaddition, light L₁₂ incident into a middle region between the center andan outer region on the left side in the drawing is diffracted to thecenter side and transmits through the optically-anisotropic layer 36 aas light L₁₃. In addition, light L₁₄ incident into the outer region onthe left side in the drawing is diffracted to the center side at alarger angle and transmits through the optically-anisotropic layer 36 aas light L₁₅.

Therefore, as shown in FIG. 14 , the optically-anisotropic layer 36 afunctions as a condenser lens that collects transmitted light.

In the liquid crystal diffraction element according to the embodiment ofthe present invention, the twisted angle of the liquid crystal compoundin the thickness direction in the optically-anisotropic layer may beappropriately set according to the single period Λ of the liquid crystalalignment pattern in a plane.

In addition, in the example shown in FIG. 1 or the like, theoptically-anisotropic layer has the concentric circular liquid crystalalignment pattern having a concentric circular shape where the onein-plane direction in which the direction of the optical axis derivedthe liquid crystal compound changes while continuously rotating movesfrom an inner side toward an outer side. However, the present inventionis not limited to this configuration.

For example, a configuration may be adopted in which the arrangementaxis D of the liquid crystal alignment pattern of theoptically-anisotropic layer has one in-plane direction, and the singleperiod Λ gradually changes in the one in-plane direction, and theaverage tilt angle of the dark portion gradually changes in the onein-plane direction.

In addition, the liquid crystal alignment pattern may be a symmetricalconcentric circular shape or an asymmetrical liquid crystal alignmentpattern from an inner side toward an outer side. In this case, thecenter of the liquid crystal alignment pattern may be different from thecenter of the liquid crystal diffraction element. The liquid crystalalignment pattern is not limited to the above-described configurationand may be appropriately set depending on the function required for theliquid crystal diffraction element.

The liquid crystal diffraction element according to the embodiment ofthe present invention can be used for various uses where transmission oflight in a direction different from an incidence direction is allowed,for example, an optical path changing member, a light collectingelement, a light diffusing element to a predetermined direction, adiffraction element, or the like in an optical device.

The liquid crystal diffraction element according to the embodiment ofthe present invention may allow transmission of visible light andrefract the transmitted light, or may refract infrared light and/orultraviolet light and allow the refracted light.

The optical element according to the embodiment of the present inventionincludes the above-described liquid crystal diffraction element and acircularly polarizing plate.

A part of circularly polarized light incident into the liquid crystaldiffraction element may transmit through the liquid crystal diffractionelement (zero-order light) without being diffracted. The circularlypolarized light that is not diffracted by the liquid crystal diffractionelement may decrease the performance depending on applications. On theother hand, by using the liquid crystal diffraction element and thecircularly polarizing plate in combination, the light (zero-order light)transmitted through the liquid crystal diffraction element without beingdiffracted can be reduced.

For example, the liquid crystal diffraction element and the circularlypolarizing plate (where a retardation plate and a linearly polarizingplate (polarizer) are disposed in this order) will be described. In acase where right circularly polarized light is incident into the liquidcrystal diffraction element, the incident right circularly polarizedlight is diffracted and emitted from the liquid crystal diffractionelement. In addition, during the diffraction, the right circularlypolarized light is converted into left circularly polarized light. Theleft circularly polarized light (that is, first-order light) that isdiffracted by the liquid crystal diffraction element is converted intolinearly polarized light by the retardation plate (¼ wave plate) of thecircularly polarizing plate. The linearly polarized light converted bythe retardation plate transmits through the linearly polarizing plateand is emitted.

Here, in a case where a part of light is not diffracted by the liquidcrystal diffraction element, a part of right circularly polarized lightincident into the liquid crystal diffraction element transmits throughthe liquid crystal diffraction element without being diffracted. In acase where the circularly polarizing plate is not provided, the rightcircularly polarized light that is not diffracted by the liquid crystaldiffraction element linearly travels as it is. The right circularlypolarized light that linearly travels is unnecessary depending onapplications, which decreases the performance.

On the other hand, as described above, a configuration where the opticalelement includes the circularly polarizing plate can also be preferablyused. In a case where the circularly polarizing plate is provided, rightcircularly polarized light (that is, zero-order light) that is notdiffracted by the liquid crystal diffraction element is incident intoand diffracted by the retardation plate of the circularly polarizingplate, is converted into linearly polarized light having a directionperpendicular to the above-described direction, and is incident into thelinearly polarizing plate and absorbed. That is, the right circularlypolarized light that is not diffracted by the liquid crystal diffractionelement is absorbed by the circularly polarizing plate. Accordingly,transmission of the desired first-order light of left circularlypolarized light is allowed, and the right circularly polarized lightthat is not diffracted can be reduced. Therefore, a decrease inperformance by unnecessary light (zero-order light) can be suppressed.

<Polarizing Plate>

The linearly polarizing plate used in the present invention is notparticularly limited as long as they are linearly polarizing plateshaving a function of allowing transmission of linearly polarized lightin one polarization direction and absorbing linearly polarized light inanother polarization direction. For example, a well-known linearlypolarizing plate in the related art can be used. The linearly polarizingplate may be an absorptive linearly polarizing plate or a reflectivelinearly polarizing plate.

As the absorptive linearly polarizing plate, for example, aniodine-based polarizer, a dye-based polarizer using a dichroic dye, or apolyene polarizer that is an absorptive polarizer can be used. As theiodine-based polarizer and the dye-based polarizer, any one of a coatingtype polarizer or a stretching type polarizer can be used. Inparticular, a polarizer prepared by absorbing iodine or a dichroic dyeon polyvinyl alcohol and performing stretching is preferable.

In addition, examples of a method of obtaining a polarizer by performingstretching and dyeing on a laminated film in which a polyvinyl alcohollayer is formed on the substrate include methods described inJP5143918B, JP5048120B, JP4691205B, JP4751481B, and JP4751486B, andwell-known techniques relating to the polarizers can be used.

As the absorptive polarizer, for example, a polarizer obtained byaligning a dichroic coloring agent using the aligning properties ofliquid crystal without performing stretching is more preferable. Thepolarizer has many advantages in that, for example, the thickness can besignificantly reduced to about 0.1 μm to 5 μm, cracks are not likely toinitiate or thermal deformation is small during folding as described inJP2019-194685A, and even a polarizing plate having a high transmittanceof higher than 50% has excellent durability as described in JP6483486B,and thermoformability is excellent.

By utilizing these advantages, the polarizer is applicable to anapplication that requires high brightness or small size and lightweight, an application of a fine optical system, or an application offorming into a portion having a curved surface, or an application of aflexible portion. In addition, a polarizer that is transferred afterpeeling a support can also be used.

In an on-board display optical system such as a head-up display, anoptical system such as AR glasses or VR glasses, an optical sensor suchas LiDAR, a face recognition system, or polarization imaging, or thelike, it is also preferable that an absorptive polarizer is incorporatedin order to prevent stray light.

As the reflective linearly polarizing plate, for example, a filmobtained by stretching a layer including two polymers or a wire gridpolarizer described in JP2011-053705A can be used. From the viewpoint ofbrightness, the film obtained by stretching the layer including polymersis preferable. As the commercially available product, for example, areflective polarizer (trade name: APF) manufactured by 3M or a wire gridpolarizer (trade name: WGF) manufactured by Asahi Kasei Corporation canbe suitably used. Alternatively, a reflective linearly polarizing plateincluding a combination of a cholesteric liquid crystal film and a λ/4plate may be used.

It is preferable that the polarizing plate used in the present inventionhas a smooth surface. In particular, in a case where the polarizingplate is applied to a lens or the like, due to the image enlargementeffect of the lens, small surface unevenness may lead to distortion ofthe image. Therefore, it is desirable that the surface does not haveunevenness. Specifically, an arithmetic average roughness Ra of thesurface is preferably 50 nm or less, more preferably 30 nm or less,still more preferably 10 nm or less, and most preferably 5 nm or less.In addition, on the surface of the polarizing plate, a difference inheight of the surface unevenness in a range of 1 square millimeter ispreferably 100 nm or less, more preferably 50 nm or less, and mostpreferably 20 nm or less.

The surface unevenness and the arithmetic average roughness can bemeasured using a roughness meter or an interferometer. For example, thesurface unevenness and the arithmetic average roughness can be measuredusing an interferometer “Vertscan” (manufactured by Mitsubishi ChemicalSystems Inc.).

<Retardation Plate>

The retardation plate used in the present invention is a retardationplate that converts the phase of incident polarized light. Theretardation plate is disposed such that a direction of a slow axis isadjusted depending on whether to convert incident polarized light intolight similar to linearly polarized light or circularly polarized light.Specifically, the retardation plate may be disposed such that an angleof a slow axis with respect to an absorption axis of a linearlypolarizing plate disposed adjacent thereto is +45° or −45°.

The retardation plate used in the present invention may be a monolayertype including one optically-anisotropic layer or a multilayer typeincluding two or more optically-anisotropic layers having different slowaxes. Examples of the multilayer type retardation plate include thosedescribed in WO13/137464A, WO2016/158300A, JP2014-209219A,JP2014-209220A, WO14/157079A, JP2019-215416A, and WO2019/160044A.However, the present invention is not limited to this example.

From the viewpoint of converting linearly polarized light intocircularly polarized light or converting circularly polarized light intolinearly polarized light, it is preferable that the retardation plate isa λ/4 plate.

The λ/4 plate is not particularly limited, and various well-known plateshaving a λ/4 function can be used. Specific examples of the λ/4 plateinclude those described in US2015/0277006A.

Specific examples of an aspect where the λ/4 plate has a monolayerstructure include a stretched polymer film and a retardation film wherean optically-anisotropic layer having a λ/4 function is provided on asupport. Examples of an aspect in which the λ/4 plate has a multi-layerstructure include a broadband λ/4 plate in which a λ/4 plate and a λ/2wave plate are laminated.

The thickness of the λ/4 plate is not particularly limited and ispreferably 1 to 500 μm, more preferably 1 to 50 μm, and still morepreferably 1 to 5 μm.

It is preferable that the retardation plate used in the presentinvention has reverse wavelength dispersibility. By having reversewavelength dispersibility, a phase change in the retardation plate isideal, and conversion between linearly polarized light and circularlypolarized light is ideal.

In the configuration where the liquid crystal diffraction elementaccording to the embodiment of the present invention and the circularlypolarizing plate are used in combination, another optical element thatis provided downstream of the circularly polarizing plate may also beused in combination.

For example, a retardation plate may be disposed downstream of thecircularly polarizing plate. Specifically, a configuration wherelinearly polarized light transmitted through the circularly polarizingplate (where the retardation plate and the linearly polarizing plate aredisposed in this order) is converted into circularly polarized light,elliptically polarized light, and linearly polarized light having adifferent polarization direction by the retardation plate that isdisposed downstream of the circularly polarizing plate can also bepreferably used. In addition, instead of the retardation plate, adepolarization layer that depolarizes the polarization state of light inat least a part of a wavelength range may be used. As the depolarizationlayer, for example, a high retardation film (having an in-planeretardation of 3000 nm or more) or a light scattering layer can be used.By controlling the polarization state of the light emitted from thecircularly polarizing plate, the polarization state can be adjusteddepending on applications.

In another example, an optical element that is provided downstream ofthe circularly polarizing plate to deflect light may be used. Forexample, by disposing the optical element such as a lens that deflectslight downstream of the circularly polarizing plate, the travelingdirection of light emitted from the circularly polarizing plate can bechanged. By controlling the deflection direction of the light emittedfrom the circularly polarizing plate, the emission direction of lightcan be adjusted depending on applications.

<Adhesive Layer (Pressure Sensitive Adhesive Layer), Adhesive>

The optical film may include an adhesive layer for adhesion of therespective layers. In the present specification, “adhesive” is used as aconcept including “pressure-sensitive adhesive”.

Examples of the adhesive include a water-soluble adhesive, anultraviolet curable adhesive, an emulsion type adhesive, a latex typeadhesive, a mastic adhesive, a multi-layered adhesive, a paste-likeadhesive, a foaming adhesive, a supported film adhesive, a thermoplasticadhesive, a hot-melt adhesive, a thermally solidified adhesive, athermally activated adhesive, a heat-seal adhesive, a thermosettingadhesive, a contact type adhesive, a pressure-sensitive adhesive, apolymerizable adhesive, a solvent type adhesive, a solvent-activatedadhesive, and a ceramic adhesive. Specifically, for example, a boroncompound aqueous solution, a curable adhesive of an epoxy compound nothaving an aromatic ring in a molecule as disclosed in JP2004-245925A, anactive energy ray-curable adhesive having a molar absorption coefficientof 400 or higher at a wavelength of 360 to 450 nm and including aphotopolymerization initiator and an ultraviolet curable compound asessential components as described in JP2008-174667A, or an active energyray-curable adhesive including (a) a (meth)acrylic compound having twoor more (meth)acryloyl groups in a molecule, (b) a (meth)acryliccompound having a hydroxyl group and only one polymerizable double bondin a molecule, and (c) a phenol ethylene oxide modified acrylate or anonyl phenol ethylene oxide modified acrylate with respect to 100 partsby mass of the total amount of the (meth)acrylic compounds as describedin JP2008-174667A can be used. Optionally, various adhesives can be usedalone or as a mixture of two or more kinds.

In the laminated optical film, from the viewpoint of reducingunnecessary reflection, it is preferable that a difference in refractiveindex between the adhesive layer and a layer adjacent thereto is small.Specifically, the difference in refractive index from the adjacent layeris preferably 0.05 or less and more preferably 0.01 or less. A method ofadjusting the refractive index of the adhesive layer is not particularlylimited. For example, an existing method such as a method of adding offine particles of zirconia, silica, acryl, acrylic-styrene, melamine, orthe like, a method of adjusting the refractive index of a resin, or amethod described in JP1999-223712A (JP-H11-223712A) can be used.

In addition, in a case where the adjacent layer has refractive indexanisotropy in a plane, it is preferable that the difference inrefractive index from the adjacent layer in all of the in-planedirections is 0.05 or less. Therefore, the adhesive layer may haverefractive index anisotropy in a plane.

In a case where a difference in refractive index between adhesioninterfaces is large, the interface reflectivity can be reduced bygenerating a refractive index distribution in the thickness direction ofthe adhesive layer. Examples of a method of generating a refractiveindex distribution in the thickness direction include a method ofproviding a plurality of adhesive layers, a method of mixing interfacesbetween a plurality adhesive layers that are provided, and a method ofcontrolling an uneven distribution state of a material in the adhesivelayer to generate a refractive index distribution.

In addition, the adhesive layer can be provided on one member or bothmembers to be bonded using any method such as application, vapordeposition, or transfer. From the viewpoint of increasing the adhesionstrength, a post-treatment such as a heating treatment or ultravioletirradiation can be performed according to the kind of the adhesive. Thethickness of the adhesive layer can be freely adjusted and is preferably20 μm or less and more preferably 0.1 μm or less. Examples of a methodof forming the adhesive layer having a thickness of 0.1 μm or lessinclude a method of vapor-depositing a ceramic adhesive such as siliconoxide (SiO_(x) layer) on a bonding surface. For the bonding surface ofthe bonding member, before the bonding, for example, a surface reformingtreatment such as a plasma treatment, a corona treatment, or asaponification treatment can be performed, and a primer layer can beapplied. In addition, in a case where a plurality of bonding surfacesare present, the kind, thickness, and the like of the adhesive layer canbe adjusted for each of the bonding surfaces.

<Cutting of Laminate>

The prepared laminate can be cut into a predetermined size. A method ofcutting the laminate is not particularly limited. For example, variouswell-known methods such as a method of physically cutting the laminateusing a blade such as a Thomson blade or a method of cutting thelaminate by laser irradiation can be used. In a case where laser lightis used, it is preferable to select a pulse duration (nanosecond,picosecond, or femtosecond) and a wavelength in consideration of damageto cutting properties and a material. In addition, after processing thelaminate in a predetermined shape, for example, edge surface polishingmay be performed.

From the viewpoint of, for example, improving the workability during thecutting or suppressing dust emission, the cutting can also be performedin a state where a peelable protective film is attached. In addition, byperforming the cutting while observing the liquid crystal alignmentpattern, for example, using a method described in JP2004-141889A, acutting position can be freely determined. In this case, in order toeasily see the liquid crystal alignment pattern, the liquid crystalalignment pattern can also be observed through a polarizing plate, aretardation film, or the like. In addition, in a case where a pluralityof optical elements are provided on one substrate, it is preferable thatthe plurality of optical elements are cut at the same time.

<Other Treatments>

For example, on order to accurately provide the laminate in a device orto improve the accuracy of an axis or a cutting position during thecutting, a mark having a given shape can be optionally formed. The kindof the mark can be freely selected, and a method of physically formingthe mark using a laser, an ink jet method, or the like, a method ofpartially changing the liquid crystal alignment state, or a method offorming a region that is partially decolored or colored can be selected.

In addition, in order to protect the liquid crystal layer, optionally, aprotective layer (for example, a gas barrier layer, a layer for blockingmoisture or the like, an ultraviolet absorbing layer, or a scratchresistance layer) can be provided. The protective layer can be formed onthe liquid crystal layer directly or through a pressure sensitiveadhesive layer or another optical film. In order to reduce thereflectivity of the surface, an antireflection layer (for example, an LRlayer, an AR layer, or a moth eye layer) may be provided. Variousprotective layers can be appropriately selected from well-knownprotective layers. In a case where the gas barrier layer is providedpolyvinyl alcohol is preferable. The polyvinyl alcohol can also have afunction as a polarizer. In addition, the ultraviolet absorbing layer isa layer including an ultraviolet absorber. As the ultraviolet absorber,from the viewpoints of excellent capability to absorb ultraviolet lighthaving a wavelength of 370 nm or less and excellent display properties,an ultraviolet absorber having small absorption of visible light havinga wavelength of 400 nm or more is preferably used. As the ultravioletabsorber, one kind may be used alone, or two or more kinds may be usedin combination. Examples of the ultraviolet absorber include ultravioletabsorbers described in JP2001-72782A and JP2002-543265A. Specificexamples of the ultraviolet absorber include an oxybenzophenonecompound, a benzotriazole compound, a salicylic acid ester compound, abenzophenone compound, a cyanoacrylate compound, and a nickel complexsalt compound.

<Combination of Plurality of Liquid Crystal Diffraction Elements>

The liquid crystal diffraction element according to the embodiment ofthe present invention can be used as a combination of a plurality ofliquid crystal diffraction elements.

For example, by combining a plurality of liquid crystal diffractionelements and changing the polarization states incident into liquidcrystal diffraction elements as disclosed in Optics Express, Vol. 28, No16/3 Aug. 2020, the collecting properties/diverging properties ofemitted light can be switched between a plurality of combinations.

By combining the plurality of liquid crystal diffraction elements,display (foveated display) corresponding to fovea centralis can beperformed in an HMD such as AR glasses or VR glasses.

<Combination with Phase Modulation Element>

A configuration where the liquid crystal diffraction element accordingto the embodiment of the present invention is used in combination with aphase modulation element can also be preferably used.

For example, by using a switchable λ/2 plate (half waveplate) that canmodulate a retardation with a voltage as disclosed in U.S. Ser. No.10/379,419B and the liquid crystal diffraction element according to theembodiment of the present invention (used as a passive element) incombination, a focus tunable lens having a high diffraction efficiencyirrespective of light incidence positions in a plane of the element canbe realized. In addition, by using plural sets of the phase modulationelements and the liquid crystal diffraction elements in combination, aplurality of adjustable focal lengths can increase.

By using this focus tunable lens for AR glasses or VR glasses, the focalposition of a display image of an HMD can be freely changed.

<Combination with Lens>

A configuration where the liquid crystal diffraction element accordingto the embodiment of the present invention is used in combination withanother lens element can also be preferably used.

For example, by using the liquid crystal diffraction element accordingto the embodiment of the present invention in combination with a Fresnellens disclosed in SID 2020 DIGEST, 40-4, pp. 579-582, chromaticaberration of the lens can be improved with a high diffractionefficiency irrespective of light incidence positions in a plane of theelement. The lens to be used in combination is not particularly limited,and a combination with a refractive index lens or a pancake lensdisclosed in U.S. Pat. No. 3,443,858A, Optics Express, Vol. 29, No 4/15Feb. 2021, or the like can also be suitably used.

By using an optical system including the lens and the liquid crystaldiffraction element in combination for AR glasses or VR glasses, colorshift (chromatic aberration of the lens) of a display image of the HMDcan be improved.

<Combination with Light Guide Plate>

A configuration where the liquid crystal diffraction element accordingto the embodiment of the present invention is used in combination with alight guide plate can also be preferably used.

For example, in a combination of a light guide plate and a lensdisclosed in Proc. of SPIE Vol. 11062, Digital Optical Technologies2019, 110620J (16 Jul. 2019), by using the liquid crystal diffractionelement according to the embodiment of the present invention as thelens, the focal position of a display image emitted from the light guideplate can be changed.

This way, by using the liquid crystal diffraction element in combinationwith the light guide plate, the focal position of a display image of anHMD such as AR glasses or VR glasses can be adjusted. For use in ARglasses, by using the liquid crystal diffraction element according tothe embodiment of the present invention as positive and negative lensesbetween which a light guide plate is interposed as disclosed in Proc. ofSPIE Vol. 11062, Digital Optical Technologies 2019, 110620J (16 Jul.2019), both of an actual scene and a display image output from the lightguide plate can be observed without distortion.

<Combination with Image Display Apparatus>

A combination of the liquid crystal diffraction element according to theembodiment of the present invention with an image display apparatus canalso be preferably used.

For example, by using the liquid crystal diffraction element (used as adiffractive deflection film) and an image display apparatus disclosed inCrystals 2021, 11, 107 in combination, a brightness distribution ofemitted light from the image display apparatus can be adjusted.

By using the image display unit combined with the image displayapparatus, a brightness distribution of an HMD such as AR glasses or VRglasses can be suitably adjusted.

<Combination with Beam Steering>

A combination of the liquid crystal diffraction element according to theembodiment of the present invention with a light deflection element(beam steering) can also be preferably used.

For example, by using the liquid crystal diffraction element accordingto the embodiment of the present invention as a diffraction element of alight deflection element disclosed in WO2019/189675A, the deflectionangle of emitted light can be increased with a high diffractionefficiency.

By using the liquid crystal diffraction element in combination with thelight deflection element (beam steering), a light irradiation angle of adistance-measuring sensor such as light detection and ranging (LIDAR)can be suitably widened.

Hereinabove, the liquid crystal diffraction element, the opticalelement, the image display unit, the head-mounted display, the beamsteering, and the sensor according to the embodiment of the presentinvention have been described in detail. However, the present inventionis not limited to the above-described examples, and various improvementsand modifications can be made within a range not departing from thescope of the present invention.

EXAMPLES

Hereinafter, the characteristics of the present invention will bedescribed in detail using examples. Materials, chemicals, used amounts,material amounts, ratios, treatment details, treatment procedures, andthe like shown in the following examples can be appropriately changedwithin a range not departing from the scope of the present invention.Accordingly, the scope of the present invention is not limited to thefollowing specific examples.

Comparative Example 1

<Preparation of Liquid Crystal Diffraction Element>

(Support)

A glass substrate was used as the support.

(Formation of Alignment Film)

The following coating liquid for forming an alignment film was appliedto the support by spin coating. The support on which the coating film ofthe coating liquid for forming an alignment film was formed was driedusing a hot plate at 60° C. for 60 seconds. As a result, an alignmentfilm was formed.

Coating Liquid for Forming Alignment Film Material A for photo-alignment 1.00 part by mass Water 16.00 parts by mass Butoxyethanol 42.00 partsby mass Propylene glycol monomethyl ether 42.00 parts by mass -MaterialA for Photo-Alignment-

(Exposure of Alignment Film)

The concentric circular alignment film was exposed using the exposuredevice shown in FIG. 11 to form an alignment film P-1 having analignment pattern.

In the exposure device, a laser that emits laser light having awavelength (325 nm) was used as the laser. The exposure amount of theinterference light was 1000 mJ/cm². By using the exposure device shownin FIG. 11 , the single period of the alignment pattern graduallydecreased from the center toward the outer direction.

(Formation of Optically-Anisotropic Layer)

As a liquid crystal composition forming a first optically-anisotropiclayer, the following composition A-1 was prepared.

Composition A-1 Liquid crystal compound L-1  100.00 parts by mass Chiralagent C-1   0.32 parts by mass Polymerization initiator (IRGACURE-OXE01, manufactured by BASF SE)   1.00 part by mass Leveling agent T-1  0.08 parts by mass Methyl ethyl ketone 1050.00 parts by mass LiquidCrystal Compound L-1

Chiral Agent C-1

Leveling Agent T-1

The optically-anisotropic layer was formed by applying multiple layersof the composition A-1 to the alignment film P-1. The application of themultiple layers refers to repetition of the following processesincluding: preparing a first liquid crystal immobilized layer byapplying the composition A-1 for forming the first layer to thealignment film, heating the composition A-1, and irradiating thecomposition A-1 with ultraviolet light for curing; and preparing asecond or subsequent liquid crystal immobilized layer by applying thecomposition A-1 for forming the second or subsequent layer to the formedliquid crystal immobilized layer, heating the composition A-1, andirradiating the composition A-1 with ultraviolet light for curing asdescribed above. Even in a case where the liquid crystal layer wasformed by the application of the multiple layers such that the totalthickness of the optically-anisotropic layer was large, the alignmentdirection of the alignment film was reflected from a lower surface ofthe optically-anisotropic layer to an upper surface thereof.

Regarding the first liquid crystal layer, the following composition A-1was applied to the alignment film P-1 to form a coating film, thecoating film was heated to 80° C. using a hot plate, the coating filmwas irradiated with ultraviolet light having a wavelength of 365 nm atan irradiation dose of 300 mJ/cm² using a high-pressure mercury lamp ina nitrogen atmosphere. As a result, the alignment of the liquid crystalcompound was immobilized.

Regarding the second or subsequent liquid crystal immobilized layer, thecomposition was applied to the first liquid crystal layer, and theapplied composition was heated and irradiated with ultraviolet light forcuring under the same conditions as described above. As a result, aliquid crystal immobilized layer was prepared. This way, by repeatingthe application multiple times until the total thickness reached adesired film thickness, an optically-anisotropic layer was obtained, anda liquid crystal diffraction element was prepared.

A complex refractive index of the cured layer of a liquid crystalcomposition A-1 was obtained by applying the liquid crystal compositionA-1 a support with an alignment film for retardation measurement thatwas prepared separately, aligning the director of the liquid crystalcompound to be parallel to the substrate, irradiating the liquid crystalcompound with ultraviolet irradiation for immobilization to obtain aliquid crystal immobilized layer (cured layer), and measuring theretardation value and the film thickness of the liquid crystalimmobilized layer. Δn can be calculated by dividing the retardationvalue by the film thickness. The retardation value was measured at adesired wavelength using Axoscan (manufactured by Axometrix Inc.), andthe film thickness was measured using a scanning electron microscope(SEM).

Finally, in the optically-anisotropic layer, Δn₅₅₀×Thickness (Re(550))of the liquid crystals was 275 nm, and it was verified using apolarization microscope that concentric circular (radial) periodicalignment occurred on the surface as shown in FIG. 2 . In the liquidcrystal alignment pattern of the optically-anisotropic layer, regardingthe single period over which the optical axis of the liquid crystalcompound rotated by 180°, the single period of a portion at a distanceof about 2 mm from the center was 10 μm, the single period of a portionat a distance of 25 mm from the center was 1 μm, and the single periodof a portion at a distance of 30 mm from the center was 0.6 μm. Thisway, the single period decreased toward the outer direction. Inaddition, the twisted angle in the thickness direction of theoptically-anisotropic layer was left-twisted and 70° (−70°) over theentire in-plane region. Hereinafter, unless specified otherwise,“Δn₅₅₀×d” and the like were measured as described above.

As a liquid crystal composition forming a second optically-anisotropiclayer, the following composition A-2 was prepared.

Composition A-2 Liquid crystal compound L-1  100.00 parts by mass Chiralagent C-2   0.18 parts by mass Polymerization initiator (IRGACURE-OXE01, manufactured by BASF SE)   1.00 part by mass Leveling agent T-1  0.08 parts by mass Methyl ethyl ketone 1050.00 parts by mass ChiralAgent C-2

A second optically-anisotropic layer was formed using the same method asthat of the first optically-anisotropic layer, except that the filmthickness of the optically-anisotropic layer was adjusted using thecomposition A-2.

Finally, in the optically-anisotropic layer, Δn₅₅₀×Thickness (Re(550))of the liquid crystals was 275 nm, and it was verified using apolarization microscope that concentric circular (radial) periodicalignment occurred on the surface as shown in FIG. 2 . In the liquidcrystal alignment pattern of the optically-anisotropic layer, the perioddecreased toward the outer direction. The twisted angle in the thicknessdirection of the optically-anisotropic layer was right-twisted and 70°in a plane.

Example 1

(Formation of Optically-Anisotropic Layer)

As a liquid crystal composition forming an optically-anisotropic layer,the following compositions B-1, B-2, and B-3 were prepared.

Composition B1 Liquid crystal compound L-1  100.00 parts by mass Chiralagent C-3   0.23 parts by mass Chiral agent C-4   0.82 parts by massPolymerization initiator (IRGACURE-OXE 01, manufactured by BASF SE)  1.00 part by mass Leveling agent T-1   0.08 parts by mass Methyl ethylketone 1050.00 parts by mass Chiral Agent C-3

Chiral Agent C-4

As the liquid crystal composition for forming the secondoptically-anisotropic layer, a composition B-2 was prepared using thesame method as that of the composition B-1 according to Example 1,except that the amount of chiral agent C-3 was changed to 0.54 parts bymass and the amount of the chiral agent C-4 was changed to 0.62 parts bymass.

As the liquid crystal composition for forming the thirdoptically-anisotropic layer, a composition B-3 was prepared using thesame method as that of the composition B-1 according to Example 1,except that the amount of chiral agent C-3 was changed to 0.48 parts bymass and the chiral agent C-4 was not added.

First, a first region was formed by applying multiple layers of thecomposition B-1 to the alignment film P-1. The application of themultiple layers refers to repetition of the following processesincluding: preparing a first liquid crystal immobilized layer byapplying the first layer-forming composition B-1 to the alignment film,heating the composition B-1, cooling the composition B-1, andirradiating the composition B-1 with ultraviolet light for curing; andpreparing a second or subsequent liquid crystal immobilized layer byapplying the second or subsequent layer-forming composition B-1 to theformed liquid crystal immobilized layer, heating the composition B-1,cooling the composition B-1, and irradiating the composition B-1 withultraviolet light for curing as described above. Even in a case wherethe liquid crystal layer was formed by the application of the multiplelayers such that the total thickness of the optically-anisotropic layerwas large, the alignment direction of the alignment film was reflectedfrom a lower surface of the optically-anisotropic layer to an uppersurface thereof.

First, in order to form the first layer, the composition B-1 was appliedto the alignment film P-1, and the coating film was heated to 80° C. ona hot plate. Next, the coating film was irradiated with ultravioletlight having a wavelength of 365 nm using a LED-UV exposure device. Atthis time, the coating film was irradiated while changing theirradiation dose of ultraviolet light in a plane. Specifically, thecoating film was irradiated by changing the irradiation dose in a planesuch that the irradiation dose increased from the center portion towardan end part. Next, the coating film heated on a hot plate at 80° C. wasirradiated with ultraviolet light having a wavelength of 365 nm at anirradiation dose of 300 mJ/cm² using a high-pressure mercury lamp in anitrogen atmosphere. As a result, the alignment of the liquid crystalcompound was immobilized.

Regarding the second or subsequent liquid crystal layer, the compositionwas applied to the liquid crystal immobilized layer, and then a liquidcrystal immobilized layer was prepared under the same conditions asdescribed above. This way, by repeating the application multiple timesuntil the film thickness reached a desired thickness, the first regionof the optically-anisotropic layer was obtained.

Finally, in the first region, Δn₅₅₀×Thickness (Re(550)) of the liquidcrystals was 160 nm, and it was verified using a polarization microscopethat concentric circular (radial) periodic alignment occurred on thesurface as shown in FIG. 2 . In the liquid crystal alignment pattern ofthe optically-anisotropic layer, regarding the single period over whichthe optical axis of the liquid crystal compound rotated by 180°, thesingle period of a portion at a distance of about 2 mm from the centerwas 10 μm, the single period of a portion at a distance of 25 mm fromthe center was 1 μm, and the single period of a portion at a distance of30 mm from the center was 0.6 μm. This way, the single period decreasedtoward the outer direction. Regarding the twisted angle in the thicknessdirection of the optically-anisotropic layer, the twisted angle at theposition at a distance of about 2 mm from the center was left-twistedand 80° (−80°), the single period at the position at a distance of about25 mm from the center was left-twisted and 115° (−115°), and the twistedangle increased toward the outer direction.

As a result, the optically-anisotropic layer where the twisted anglechanged in a plane was formed.

Next, a second region was formed by applying multiple layers of thecomposition B-2 to the first region.

The composition B-2 was applied to the first region, and theoptically-anisotropic layer was formed using the same method as that ofthe first region according to Example 1, except that the irradiationdose of ultraviolet light with which the coating film was irradiatedchanged from the center portion toward the end part (the irradiationdose increased from the center portion toward the end part) such thatthe total thickness was a desired film thickness.

Regarding the second or subsequent liquid crystal layer, the compositionwas applied to the liquid crystal immobilized layer, and then a liquidcrystal immobilized layer was prepared under the same conditions asdescribed above. This way, by repeating the application multiple timesuntil the film thickness reached a desired thickness, the second regionof the optically-anisotropic layer was obtained.

Finally, in the second region, Δn₅₅₀×Thickness (Re(550)) of the liquidcrystals was 335 nm, and it was verified using a polarization microscopethat concentric circular (radial) periodic alignment occurred on thesurface as shown in FIG. 2 . In the liquid crystal alignment pattern ofthe optically-anisotropic layer, regarding the single period over whichthe optical axis of the liquid crystal compound rotated by 180°, thesingle period of a portion at a distance of about 2 mm from the centerwas 10 μm, the single period of a portion at a distance of 25 mm fromthe center was 1 μm, and the single period of a portion at a distance of30 mm from the center was 0.6 μm. This way, the single period decreasedtoward the outer direction. Regarding the twisted angle in the thicknessdirection of the optically-anisotropic layer, the twisted angle at theposition at a distance of about 2 mm from the center was 0°, the singleperiod at the position at a distance of about 25 mm from the center wasleft-twisted and 76° (−76°), and the twisted angle increased toward theouter direction.

As a result, the optically-anisotropic layer where the twisted anglechanged in a plane was formed.

Next, a third region was formed by applying multiple layers of thecomposition B-3 to the second region.

The composition B-3 was applied to the second region, and theoptically-anisotropic layer was formed using the same method as that ofthe first region according to Example 1, except that the irradiationdose of ultraviolet light with which the coating film was irradiatedchanged from the center portion toward the end part (the irradiationdose increased from the center portion toward the end part) such thatthe total thickness was a desired film thickness.

Regarding the second or subsequent liquid crystal layer, the compositionwas applied to the liquid crystal immobilized layer, and then a liquidcrystal immobilized layer was prepared under the same conditions asdescribed above. This way, by repeating the application multiple timesuntil the film thickness reached a desired thickness, the third regionof the optically-anisotropic layer was obtained.

Finally, in the third region, Δn₅₅₀×Thickness (Re(550)) of the liquidcrystals was 160 nm, and it was verified using a polarization microscopethat concentric circular (radial) periodic alignment occurred on thesurface as shown in FIG. 2 . In the liquid crystal alignment pattern ofthe optically-anisotropic layer, regarding the single period over whichthe optical axis of the liquid crystal compound rotated by 180°, thesingle period of a portion at a distance of about 2 mm from the centerwas 10 μm, the single period of a portion at a distance of 25 mm fromthe center was 1 μm, and the single period of a portion at a distance of30 mm from the center was 0.6 μm. This way, the single period decreasedtoward the outer direction. Regarding the twisted angle in the thicknessdirection of the optically-anisotropic layer, the twisted angle at theposition at a distance of about 2 mm from the center was right-twistedand 80° (twisted angle: 80°), the twisted angle at the position at adistance of about 25 mm from the center was left-twisted and 48°(twisted angle: 48°), and the twisted angle decreased toward the outerdirection.

As a result, the optically-anisotropic layer including the three regionswas formed.

In a case where a cross-section of the prepared optically-anisotropiclayer was observed with an SEM, bright portions and dark portions had ashape shown in FIG. 1 . That is, the dark portion had two inflectionpoints and the average tilt angle was substantially 0° at the center andincreased from the center toward the outer direction.

Example 2

(Formation of Optically-Anisotropic Layer)

As the liquid crystal composition for forming the optically-anisotropiclayer, compositions C-1, C-2, C-3, and C-4 were prepared using the samemethod as that of the composition B-1 according to Example 1, exceptthat the addition amounts of the chiral agent C-3 and the chiral agentC-4 were appropriately changed.

First, a first region was formed by applying multiple layers of thecomposition C-1 to the alignment film P-1.

The composition C-1 was applied to the alignment film P-1, and a firstregion of the optically-anisotropic layer was formed using the samemethod as that of the first optically-anisotropic layer according toExample 1, except that the irradiation dose of ultraviolet light withwhich the coating film was irradiated changed from the center portiontoward the end part such that the total thickness was a desired filmthickness.

Finally, in this region, Δn₅₅₀×Thickness (Re(550)) of the liquidcrystals was 190 nm, and it was verified using a polarization microscopethat concentric circular (radial) periodic alignment occurred on thesurface as shown in FIG. 2 . In the liquid crystal alignment pattern ofthe optically-anisotropic layer, regarding the single period over whichthe optical axis of the liquid crystal compound rotated by 180°, thesingle period of a portion at a distance of about 2 mm from the centerwas 10 μm, the single period of a portion at a distance of 25 mm fromthe center was 1 μm, and the single period of a portion at a distance of30 mm from the center was 0.6 μm. This way, the single period decreasedtoward the outer direction. Regarding the twisted angle in the thicknessdirection of the first region of the optically-anisotropic layer, thetwisted angle at the position at a distance of about 2 mm from thecenter was left-twisted and 87° (−87°), the single period at theposition at a distance of about 25 mm from the center was left-twistedand 115° (−115°), and the twisted angle increased toward the outerdirection.

Next, a second region was formed by applying multiple layers of thecomposition C-2 to the first region.

The composition C-2 was applied to the first region, and the secondregion was formed using the same method as that of the first regionaccording to Example 1, except that the irradiation dose of ultravioletlight with which the coating film was irradiated changed from the centerportion toward the end part such that the total thickness was a desiredfilm thickness.

Finally, in this region, Δn₅₅₀×Thickness (Re(550)) of the liquidcrystals was 150 nm, and it was verified using a polarization microscopethat concentric circular (radial) periodic alignment occurred on thesurface as shown in FIG. 2 . In the liquid crystal alignment pattern ofthe optically-anisotropic layer, regarding the single period over whichthe optical axis of the liquid crystal compound rotated by 180°, thesingle period of a portion at a distance of about 2 mm from the centerwas 10 μm, the single period of a portion at a distance of 25 mm fromthe center was 1 μm, and the single period of a portion at a distance of30 mm from the center was 0.6 μm. This way, the single period decreasedtoward the outer direction. Regarding the twisted angle in the thicknessdirection of the second region of the optically-anisotropic layer, thetwisted angle at the position at a distance of about 2 mm from thecenter was right-twisted and 14° (−14°), the single period at theposition at a distance of about 25 mm from the center was left-twistedand 18° (−18°), and the twisted angle changed toward the outerdirection.

Next, a third region was formed by applying multiple layers of thecomposition C-3 to the second region.

The composition C-3 was applied to the second region, and a third regionwas formed using the same method as that of the first region accordingto Example 1, except that the irradiation dose of ultraviolet light withwhich the coating film was irradiated changed from the center portiontoward the end part such that the total thickness was a desired filmthickness.

Finally, in this region, Δn₅₅₀×Thickness (Re(550)) of the liquidcrystals was 150 nm, and it was verified using a polarization microscopethat concentric circular (radial) periodic alignment occurred on thesurface as shown in FIG. 2 . In the liquid crystal alignment pattern ofthe optically-anisotropic layer, regarding the single period over whichthe optical axis of the liquid crystal compound rotated by 180°, thesingle period of a portion at a distance of about 2 mm from the centerwas 10 μm, the single period of a portion at a distance of 25 mm fromthe center was 1 μm, and the single period of a portion at a distance of30 mm from the center was 0.6 μm. This way, the single period decreasedtoward the outer direction. Regarding the twisted angle in the thicknessdirection of the third region of the optically-anisotropic layer, thetwisted angle at the position at a distance of about 2 mm from thecenter was left-twisted and 14° (−14°), the single period at theposition at a distance of about 25 mm from the center was left-twistedand 8° (−8°), and the twisted angle decreased toward the outerdirection.

Next, a fourth region was formed by applying multiple layers of thecomposition C-4 to the third region.

The composition C-4 was applied to the third region, and the fourthregion was formed using the same method as that of the first regionaccording to Example 1, except that the irradiation dose of ultravioletlight with which the coating film was irradiated changed from the centerportion toward the end part such that the total thickness was a desiredfilm thickness.

Finally, in this region, Δn₅₅₀×Thickness (Re(550)) of the liquidcrystals was 190 nm, and it was verified using a polarization microscopethat concentric circular (radial) periodic alignment occurred on thesurface as shown in FIG. 2 . In the liquid crystal alignment pattern ofthe optically-anisotropic layer, regarding the single period over whichthe optical axis of the liquid crystal compound rotated by 180°, thesingle period of a portion at a distance of about 2 mm from the centerwas 10 μm, the single period of a portion at a distance of 25 mm fromthe center was 1 μm, and the single period of a portion at a distance of30 mm from the center was 0.6 μm. This way, the single period decreasedtoward the outer direction. Regarding the twisted angle in the thicknessdirection of the fourth region of the optically-anisotropic layer, thetwisted angle at the position at a distance of about 2 mm from thecenter was right-twisted and 87°, the single period at the position at adistance of about 25 mm from the center was right-twisted and 237°, andthe twisted angle increased toward the outer direction.

As a result, the optically-anisotropic layer including the four regionswas formed.

In a case where a cross-section of the prepared optically-anisotropiclayer was observed with an SEM, bright portions and dark portions had ashape shown in FIG. 5 . That is, the dark portion had three inflectionpoints and the average tilt angle was substantially 0° at the center andincreased from the center toward the outer direction.

Example 3

(Formation of Optically-Anisotropic Layer)

As the liquid crystal composition for forming the optically-anisotropiclayer, compositions D-1, D-2, and D-3 were prepared using the samemethod as that of the composition B-1 according to Example 1, exceptthat the addition amounts of the chiral agent C-3 and the chiral agentC-4 were appropriately changed.

First, a first region was formed by applying multiple layers of thecomposition D-1 to the alignment film P-1. Next, a second region wasformed by applying multiple layers of the composition D-2 to the firstregion. Next, a third region was formed by applying multiple layers ofthe composition D-3 to the second region.

Each of the regions was formed, and the optically-anisotropic layer wasformed using the same method as that of the first region according toExample 1, except that the irradiation dose of ultraviolet light withwhich the coating film was irradiated changed from the center portiontoward the end part such that the total thickness was a desired filmthickness.

It was verified using a polarization microscope that the preparedoptically-anisotropic layer had a periodically aligned surface having aconcentric circular shape (radial shape) as shown in FIG. 2 . In theliquid crystal alignment pattern of the optically-anisotropic layer,regarding the single period over which the optical axis of the liquidcrystal compound rotated by 180°, the single period of a portion at adistance of about 2 mm from the center was 10 μm, the single period of aportion at a distance of 25 mm from the center was 1 μm, and the singleperiod of a portion at a distance of 30 mm from the center was 0.6 μm.This way, the single period decreased toward the outer direction.

In the first region of the optically-anisotropic layer, finally,Δn₅₅₀×Thickness (Re(550)) of the liquid crystal was 150 nm, andRegarding the twisted angle in the thickness direction, the twistedangle at the position at a distance of about 2 mm from the center wasleft-twisted and 83° (−83°), the twisted angle at the position at adistance of about 25 mm from the center was left-twisted and 114°(−114°), the twisted angle at the position at a distance of about 30 mmfrom the center was left-twisted and 161° (−161°), and the twisted angleincreased toward the outer direction.

In the second region of the optically-anisotropic layer, finally,Δn₅₅₀×Thickness (Re(550)) of the liquid crystal was 335 nm, andRegarding the twisted angle in the thickness direction, the twistedangle at the position at a distance of about 2 mm from the center wasleft-twisted and 8° (−8°), the twisted angle at the position at adistance of about 25 mm from the center was left-twisted and 85° (−85°),the twisted angle at the position at a distance of about 30 mm from thecenter was left-twisted and 137° (−137°), and the twisted angleincreased toward the outer direction.

In the third region of the optically-anisotropic layer, finally,Δn₅₅₀×Thickness (Re(550)) of the liquid crystal was 170 nm, andRegarding the twisted angle in the thickness direction, the twistedangle at the position at a distance of about 2 mm from the center wasright-twisted and 78°, the twisted angle at the position at a distanceof about 25 mm from the center was right-twisted and 41°, the twistedangle at the position at a distance of about 30 mm from the center wasright-twisted and 19°, and the twisted angle decreased toward the outerdirection.

As a result, the optically-anisotropic layer including the three regionswas formed.

In a case where a cross-section of the prepared optically-anisotropiclayer was observed with an SEM, bright portions and dark portions had ashape shown in FIG. 1 . That is, the dark portion had two inflectionpoints and the average tilt angle increased from the center toward theouter direction.

Example 4

(Formation of Optically-Anisotropic Layer)

As the liquid crystal composition forming the optically-anisotropiclayer, compositions E-1, E-2, and E-3 were prepared using the samemethod as that of the composition B-1 according to Example 1, exceptthat the amount of the liquid crystal compound L-1 was changed to 10parts by mass, the amount of the liquid crystal compound L-2 was changedto 90 parts by mass, and the addition amounts of the chiral agents C-3,the chiral agent C-4, and the leveling agent T-1 were appropriatelychanged.

First, a first region was formed by applying multiple layers of thecomposition E-1 to the alignment film P-1. Next, a second region wasformed by applying multiple layers of the composition E-2 to the firstregion. Next, a third region was formed by applying multiple layers ofthe composition E-3 to the second region.

Each of the regions was formed, and the optically-anisotropic layer wasformed using the same method as that of the first region according toExample 1, except that the irradiation dose of ultraviolet light withwhich the coating film was irradiated changed from the center portiontoward the end part such that the total thickness was a desired filmthickness.

It was verified using a polarization microscope that the preparedoptically-anisotropic layer had a periodically aligned surface having aconcentric circular shape (radial shape) as shown in FIG. 2 . In theliquid crystal alignment pattern of the optically-anisotropic layer,regarding the single period over which the optical axis of the liquidcrystal compound rotated by 180°, the single period of a portion at adistance of about 2 mm from the center was 10 μm, the single period of aportion at a distance of 25 mm from the center was 1 μm, and the singleperiod of a portion at a distance of 30 mm from the center was 0.6 μm.This way, the single period decreased toward the outer direction.

In the first region of the optically-anisotropic layer, finally,Δn₅₅₀×Thickness (Re(550)) of the liquid crystal was 150 nm, andRegarding the twisted angle in the thickness direction, the twistedangle at the position at a distance of about 2 mm from the center wasleft-twisted and 83° (−83°), the twisted angle at the position at adistance of about 25 mm from the center was left-twisted and 114°(−114°), the twisted angle at the position at a distance of about 30 mmfrom the center was left-twisted and 161° (−161°), and the twisted angleincreased toward the outer direction.

In the second region of the optically-anisotropic layer, finally,Δn₅₅₀×Thickness (Re(550)) of the liquid crystal was 335 nm, andRegarding the twisted angle in the thickness direction, the twistedangle at the position at a distance of about 2 mm from the center wasleft-twisted and 8° (−8°), the twisted angle at the position at adistance of about 25 mm from the center was left-twisted and 85° (−85°),the twisted angle at the position at a distance of about 30 mm from thecenter was left-twisted and 137° (−137°), and the twisted angleincreased toward the outer direction.

In the third region of the optically-anisotropic layer, finally,Δn₅₅₀×Thickness (Re(550)) of the liquid crystal was 170 nm, andRegarding the twisted angle in the thickness direction, the twistedangle at the position at a distance of about 2 mm from the center wasright-twisted and 78°, the twisted angle at the position at a distanceof about 25 mm from the center was right-twisted and 41°, the twistedangle at the position at a distance of about 30 mm from the center wasright-twisted and 19°, and the twisted angle decreased toward the outerdirection.

As a result, the optically-anisotropic layer including the three regionswas formed.

In a case where a cross-section of the prepared optically-anisotropiclayer was observed with an SEM, bright portions and dark portions had ashape shown in FIG. 1 . That is, the dark portion had two inflectionpoints and the average tilt angle increased from the center toward theouter direction.

Example 5

(Formation of Optically-Anisotropic Layer)

As a liquid crystal composition forming an optically-anisotropic layer,the following compositions F-1, F-2, and F-3 were prepared.

Composition F-1 Liquid crystal compound L-1 10.00 parts by mass Liquidcrystal compound L-2 90.00 parts by mass Chiral agent C-1 0.78 parts bymass Polymerization initiator (IRGACURE-OXE 01, 1.00 part by massmanufactured by BASF SE) Leveling agent T-1 0.22 parts by mass Methylethyl ketone 1050.00 parts by mass

A composition F-2 was prepared as a liquid crystal composition forforming a second optically-anisotropic layer by changing the amount ofthe chiral agent C-1 in the composition F-1 according to Example 5 to0.01 parts by mass.

A composition F-3 was prepared as a liquid crystal composition forforming a third optically-anisotropic layer by changing the chiral agentin the composition F-1 according to Example 5 to the following chiralagent C-5 and the addition amount of the chiral agent C-5 to 0.55 partsby mass.

First, a first region was formed by applying multiple layers of thecomposition F-1 to the alignment film P-1. Next, a second region wasformed by applying multiple layers of the composition F-2 to the firstregion. Next, a third region was formed by applying multiple layers ofthe composition F-3 to the second region.

Each of the regions was formed, and the optically-anisotropic layer wasformed using the same method as that of the first region according toExample 1, except that the irradiation dose of ultraviolet light withwhich the coating film was irradiated changed from the center portiontoward the end part such that the total thickness was a desired filmthickness.

It was verified using a polarization microscope that the preparedoptically-anisotropic layer had a periodically aligned surface having aconcentric circular shape (radial shape) as shown in FIG. 2 . In theliquid crystal alignment pattern of the optically-anisotropic layer,regarding the single period over which the optical axis of the liquidcrystal compound rotated by 180°, the single period of a portion at adistance of about 2 mm from the center was 10 μm, the single period of aportion at a distance of 25 mm from the center was 1 μm, and the singleperiod of a portion at a distance of 30 mm from the center was 0.6 μm.This way, the single period decreased toward the outer direction.

Finally, in the first region of the optically-anisotropic layer,finally, Δn₅₅₀×Thickness (Re(550)) of the liquid crystal was 197 nm, andregarding the twisted angle in the thickness direction, the twistedangle at the position at a distance of about 2 mm from the center wasleft-twisted and 91° (−91°), the twisted angle at the position at adistance of about 25 mm from the center was left-twisted and 82° (−82°),and the twisted angle changed toward the outer direction.

Finally, in the second region of the optically-anisotropic layer,finally, Δn₅₅₀×Thickness (Re(550)) of the liquid crystal was 347 nm, andregarding the twisted angle in the thickness direction, the twistedangle at the position at a distance of about 2 mm from the center wasleft-twisted and 19° (−19°), the twisted angle at the position at adistance of about 25 mm from the center was left-twisted and 13° (−13°),and the twisted angle changed toward the outer direction.

Finally, in the third region of the optically-anisotropic layer,finally, Δn₅₅₀×Thickness (Re(550)) of the liquid crystal was 195 nm, andregarding the twisted angle in the thickness direction, the twistedangle at the position at a distance of about 2 mm from the center wasright-twisted and 69°, the twisted angle at the position at a distanceof about 25 mm from the center was right-twisted and 77°, and thetwisted angle changed toward the outer direction.

As a result, the optically-anisotropic layer including the three regionswas formed.

In a case where a cross-section of the prepared optically-anisotropiclayer was observed with an SEM, the dark portion had two inflectionpoints, and the average tilt angle changed from the center toward theouter direction.

Example 6

(Formation of Optically-Anisotropic Layer)

As a liquid crystal composition forming an optically-anisotropic layer,the following compositions G-1, G-2, and G-3 were prepared.

A composition G-1 was prepared as a liquid crystal composition forforming a first optically-anisotropic layer by appropriately changingthe addition amount of the chiral agent C-5 in the composition F-3according to Example 5.

A composition G-2 was prepared as a liquid crystal composition forforming a second optically-anisotropic layer by appropriately changingthe addition amount of the chiral agent C-5 in the composition F-3according to Example 5.

A composition G-3 was prepared as a liquid crystal composition forforming a third optically-anisotropic layer by appropriately changingthe addition amount of the chiral agent C-1 in the composition F-1according to Example 5.

First, a first region was formed by applying multiple layers of thecomposition G-1 to the alignment film P-1. Next, a second region wasformed by applying multiple layers of the composition G-2 to the firstregion. Next, a third region was formed by applying multiple layers ofthe composition G-3 to the second region.

Each of the regions was formed, and the optically-anisotropic layer wasformed using the same method as that of the first region according toExample 1, except that the irradiation dose of ultraviolet light withwhich the coating film was irradiated changed from the center portiontoward the end part such that the total thickness was a desired filmthickness.

It was verified using a polarization microscope that the preparedoptically-anisotropic layer had a periodically aligned surface having aconcentric circular shape (radial shape) as shown in FIG. 2 . In theliquid crystal alignment pattern of the optically-anisotropic layer,regarding the single period over which the optical axis of the liquidcrystal compound rotated by 180°, the single period of a portion at adistance of about 2 mm from the center was 10 μm, the single period of aportion at a distance of 25 mm from the center was 1 μm, and the singleperiod of a portion at a distance of 30 mm from the center was 0.6 μm.This way, the single period decreased toward the outer direction.

Finally, in the first region of the optically-anisotropic layer,finally, Δn₅₅₀×Thickness (Re(550)) of the liquid crystal was 157 nm, andregarding the twisted angle in the thickness direction, the twistedangle at the position at a distance of about 2 mm from the center wasright-twisted and 88°, the twisted angle at the position at a distanceof about 25 mm from the center was right-twisted and 96°, and thetwisted angle changed toward the outer direction.

Finally, in the second region of the optically-anisotropic layer,finally, Δn₅₅₀×Thickness (Re(550)) of the liquid crystal was 355 nm, andregarding the twisted angle in the thickness direction, the twistedangle at the position at a distance of about 2 mm from the center wasright-twisted and 16°, the twisted angle at the position at a distanceof about 25 mm from the center was right-twisted and 40°, and thetwisted angle changed toward the outer direction.

Finally, in the third region of the optically-anisotropic layer,finally, Δn₅₅₀×Thickness (Re(550)) of the liquid crystal was 187 nm, andregarding the twisted angle in the thickness direction, the twistedangle at the position at a distance of about 2 mm from the center wasleft-twisted and 76° (−76°), the twisted angle at the position at adistance of about 25 mm from the center was left-twisted and 62° (−62°),and the twisted angle changed toward the outer direction.

As a result, the optically-anisotropic layer including the three regionswas formed.

In a case where a cross-section of the prepared optically-anisotropiclayer was observed with an SEM, the dark portion had two inflectionpoints, and the average tilt angle changed from the center toward theouter direction.

Example 7

(Formation of Optically-Anisotropic Layer)

As a liquid crystal composition forming an optically-anisotropic layer,the following compositions H-1, H-2, and H-3 were prepared.

As a liquid crystal composition forming a first optically-anisotropiclayer, a composition H-1 was prepared by changing the chiral agent inthe composition F-1 according to Example 5 to the chiral agent C-1 andthe chiral agent C-2 and appropriately changing the addition amounts ofthe chiral agent C-1 and the chiral agent C-2.

As a liquid crystal composition forming a second optically-anisotropiclayer, a composition H-2 was prepared by changing the chiral agent inthe composition F-2 according to Example 5 to the chiral agent C-1 andthe chiral agent C-2 and appropriately changing the addition amounts ofthe chiral agent C-1 and the chiral agent C-2.

A composition H-3 was prepared as a liquid crystal composition forforming a third optically-anisotropic layer by appropriately changingthe addition amount of the chiral agent C-5 in the composition F-3according to Example 5.

First, a first region was formed by applying multiple layers of thecomposition H-1 to the alignment film P-1. Next, a second region wasformed by applying multiple layers of the composition H-2 to the firstregion. Next, a third region was formed by applying multiple layers ofthe composition H-3 to the second region.

Each of the regions was formed, and the optically-anisotropic layer wasformed using the same method as that of the first region according toExample 1, except that the irradiation dose of ultraviolet light withwhich the coating film was irradiated changed from the center portiontoward the end part such that the total thickness was a desired filmthickness.

It was verified using a polarization microscope that the preparedoptically-anisotropic layer had a periodically aligned surface having aconcentric circular shape (radial shape) as shown in FIG. 2 . In theliquid crystal alignment pattern of the optically-anisotropic layer,regarding the single period over which the optical axis of the liquidcrystal compound rotated by 180°, the single period of a portion at adistance of about 2 mm from the center was 10 μm, the single period of aportion at a distance of 25 mm from the center was 1 μm, and the singleperiod of a portion at a distance of 30 mm from the center was 0.6 μm.This way, the single period decreased toward the outer direction.

Finally, in the first region of the optically-anisotropic layer,finally, Δn₅₅₀×Thickness (Re(550)) of the liquid crystal was 176 nm, andregarding the twisted angle in the thickness direction, the twistedangle at the position at a distance of about 2 mm from the center wasleft-twisted and 76° (−76°), the twisted angle at the position at adistance of about 25 mm from the center was left-twisted and 14° (−14°),and the twisted angle changed toward the outer direction.

Finally, in the second region of the optically-anisotropic layer,finally, Δn₅₅₀×Thickness (Re(550)) of the liquid crystal was 344 nm, andregarding the twisted angle in the thickness direction, the twistedangle at the position at a distance of about 2 mm from the center wasright-twisted and 10°, the twisted angle at the position at a distanceof about 25 mm from the center was right-twisted and 126°, and thetwisted angle changed toward the outer direction.

Finally, in the third region of the optically-anisotropic layer,finally, Δn₅₅₀×Thickness (Re(550)) of the liquid crystal was 154 nm, andregarding the twisted angle in the thickness direction, the twistedangle at the position at a distance of about 2 mm from the center wasright-twisted and 84°, the twisted angle at the position at a distanceof about 25 mm from the center was right-twisted and 133°, and thetwisted angle changed toward the outer direction.

As a result, the optically-anisotropic layer including the three regionswas formed.

In a case where a cross-section of the prepared optically-anisotropiclayer was observed with an SEM, the dark portion had two inflectionpoints, and the average tilt angle changed from the center toward theouter direction.

Example 8

As the liquid crystal composition forming the optically-anisotropiclayer, compositions I-1, I-2, and I-3 were prepared using the samemethod as that of the composition B-1 according to Example 1, exceptthat the amount of the liquid crystal compound L-3 was changed to 100parts by mass, and the addition amounts of the chiral agents C-3, thechiral agent C-4, and the leveling agent T-1 were appropriately changed.

First, a first region was formed by applying multiple layers of thecomposition I-1 to the alignment film P-1. Next, a second region wasformed by applying multiple layers of the composition I-2 to the firstregion. Next, a third region was formed by applying multiple layers ofthe composition I-3 to the second region.

Each of the regions was formed, and the optically-anisotropic layer wasformed using the same method as that of the first region according toExample 1, except that the irradiation dose of ultraviolet light withwhich the coating film was irradiated changed from the center portiontoward the end part and the heating temperature of the coating filmduring the formation of the optically-anisotropic layer was changed to55° C. such that the total thickness was a desired film thickness.

It was verified using a polarization microscope that the preparedoptically-anisotropic layer had a periodically aligned surface having aconcentric circular shape (radial shape) as shown in FIG. 2 . In theliquid crystal alignment pattern of the optically-anisotropic layer,regarding the single period over which the optical axis of the liquidcrystal compound rotated by 180°, the single period of a portion at adistance of about 2 mm from the center was 10 μm, the single period of aportion at a distance of 25 mm from the center was 1 μm, and the singleperiod of a portion at a distance of 30 mm from the center was 0.6 μm.This way, the single period decreased toward the outer direction.

In the first region of the optically-anisotropic layer, finally,Δn₅₅₀×Thickness (Re(550)) of the liquid crystal was 150 nm, andRegarding the twisted angle in the thickness direction, the twistedangle at the position at a distance of about 2 mm from the center wasleft-twisted and 83° (−83°), the twisted angle at the position at adistance of about 25 mm from the center was left-twisted and 114°(−114°), the twisted angle at the position at a distance of about 30 mmfrom the center was left-twisted and 161° (−161°), and the twisted angleincreased toward the outer direction.

In the second region of the optically-anisotropic layer, finally,Δn₅₅₀×Thickness (Re(550)) of the liquid crystal was 335 nm, andRegarding the twisted angle in the thickness direction, the twistedangle at the position at a distance of about 2 mm from the center wasleft-twisted and 8° (−8°), the twisted angle at the position at adistance of about 25 mm from the center was left-twisted and 85° (−85°),the twisted angle at the position at a distance of about 30 mm from thecenter was left-twisted and 137° (−137°), and the twisted angleincreased toward the outer direction.

In the third region of the optically-anisotropic layer, finally,Δn₅₅₀×Thickness (Re(550)) of the liquid crystal was 170 nm, andRegarding the twisted angle in the thickness direction, the twistedangle at the position at a distance of about 2 mm from the center wasright-twisted and 78°, the twisted angle at the position at a distanceof about 25 mm from the center was right-twisted and 41°, the twistedangle at the position at a distance of about 30 mm from the center wasright-twisted and 19°, and the twisted angle decreased toward the outerdirection.

As a result, the optically-anisotropic layer including the three regionswas formed.

In a case where a cross-section of the prepared optically-anisotropiclayer was observed with an SEM, bright portions and dark portions had ashape shown in FIG. 1 . That is, the dark portion had two inflectionpoints and the average tilt angle increased from the center toward theouter direction.

Δn₅₅₀ of the liquid crystal layers (liquid crystal compounds) in Example3 was 0.15, Δn₅₅₀ of the liquid crystal layers in Example 4 was 0.25,and Δn₅₅₀ of the liquid crystal layers in Example 8 was 0.32.

[Evaluation]

<Evaluation of Diffraction Efficiency>

In a case where light was incident into the prepared liquid crystaldiffraction element from the front (direction with an angle of 0° withrespect to the normal line), the diffraction efficiency of emitted lightwas evaluated.

Specifically, each of laser light components having output centralwavelengths of 405 nm, 450 nm, 532 nm, and 650 nm was irradiated to bevertically incident into the prepared liquid crystal diffraction elementfrom a light source. In the emitted light from the liquid crystaldiffraction element, the intensities of diffracted light (first-orderlight) diffracted in a desired direction, zero-order light (emitted inthe same direction as incidence light) emitted in the other directions,and negative first-order light (light diffracted in a −θ direction in acase where the diffraction angle of first-order light with respect tozero-order light was represented by θ) were measured using aphotodetector, and the diffraction efficiency at each of the wavelengthswas calculated from the following expression.

Diffraction Efficiency=First-Order Light/(First-Order Light+Zero-OrderLight+(Negative First-Order Light))

The average value of the diffraction efficiencies was obtained from themeasured values at the wavelengths of 405 nm, 450 nm, 532 nm, and 650nm, and the wavelength dependence of the diffraction efficiency wasevaluated based on the following standards.

Laser light was caused to be vertically incident into the circularlypolarizing plate corresponding to the wavelength of the laser light tobe converted into circularly polarized light, the circularly polarizedlight was incident into the prepared liquid crystal diffraction element,and the evaluation was performed.

In addition, in the liquid crystal alignment pattern of the preparedliquid crystal diffraction element, the evaluation was performed at twopositions including the center portion of the concentric circle and thevicinity of the concentric circle (the single period was 10 μm) and thevicinity of an end part (the single period was 1 μm).

A: the average value of the diffraction efficiencies was 95% or more.

B: the average value of the diffraction efficiencies was 90% or more andless than 95%.

C: the average value of the diffraction efficiencies was less than 90%.

The results are shown in Tables 1 and 2. In Tables 1 and 2, thediffraction angle with respect to light having a wavelength of 532 nm isshown as Diffraction Angle (532).

TABLE 1 Comparative Example 1 Example 1 Example 2 Example 3 VicinityLiquid crystal alignment Single period [μm] 10 10 10 10 of centerpattern First region Re(550) [nm] 275 160 190 150 Twisted angle [°] −70−80 −87 −83 Second region Re(550) [nm] 275 335 150 335 Twisted angle [°]70 0 14 −8 Third region Re(550) [nm] — 160 150 170 Twisted angle [°] —80 −14 78 Fourth region Re(550) [nm] — — 190 — Twisted angle [°] — — 87— Evaluation Number of inflection points of angle 1 2 3 2 Number ofinflection points where tilt 1 1 3 1 direction is folded Diffractionangle (532) [°] 3 3 3 3 Wavelength dependency of diffraction C A A Aefficiency Vicinity Liquid crystal alignment Single period [μm] 1 1 1 1of end part pattern First region Re(550) [nm] 275 160 190 150 Twistedangle [°] −70 −115 −115 −114 Second region Re(550) [nm] 275 335 150 335Twisted angle [°] 70 −76 −18 −85 Third region Re(550) [nm] — 160 150 170Twisted angle [°] — 48 −8 41 Fourth region Re(550) [nm] — — 190 —Twisted angle [°] — — 237 — Evaluation Number of inflection points ofangle 1 2 3 2 Number of inflection points where tilt 1 1 1 1 directionis folded Diffraction angle (532) [°] 32 32 32 32 Wavelength dependencyof diffraction C A A A efficiency

In Examples 5 to 7, as compared to Examples 1 to 4, circularly polarizedlight having the opposite direction was used as the incident polarizedlight to perform the evaluation. In this case, in Examples 5 to 7, ascompared to Examples 1 to 4, the diffraction direction of first-orderlight and negative first-order light was reversed (diffracted in adirection in which the sign of the light diffracted in the θ directionis reversed). In addition, in Example 7, in the vicinity of the end part(the single period was 1 μm), the incidence angle of light into theliquid crystal diffraction element was 25° to perform the evaluation. InComparative Examples of Examples 5 to 7, the same evaluation wasperformed using the liquid crystal diffraction element prepared inComparative Example 1. The results were the same as that of ComparativeExample 1 shown in Table 1.

TABLE 2 Example 4 Example 5 Example 6 Example 7 Vicinity Liquid crystalalignment Single period [μm] 10 10 10 10 of center pattern First regionRe(550) [nm] 150 197 157 176 Twisted angle [°] −83 −91 88 −76 Secondregion Re(550) [nm] 335 347 355 344 Twisted angle [°] −8 −19 16 10 Thirdregion Re(550) [nm] 170 195 187 154 Twisted angle [°] 78 69 −76 84Fourth region Re(550) [nm] — — — — Twisted angle [°] — — — — EvaluationNumber of inflection points of angle 2 2 2 2 Number of inflection pointswhere tilt 1 1 1 1 direction is folded Diffraction angle (532) [°] 3 3 33 Wavelength dependency of diffraction A A A A efficiency VicinityLiquid crystal alignment Single period [μm] 1 1 1 1 of end part patternFirst region Re(550) [nm] 150 197 157 176 Twisted angle [°] −114 −82 96−14 Second region Re(550) [nm] 335 347 355 344 Twisted angle [°] −85 −1340 126 Third region Re(550) [nm] 170 195 187 154 Twisted angle [°] 41 77−62 133 Fourth region Re(550) [nm] — — — — Twisted angle [°] — — — —Evaluation Number of inflection points of angle 2 2 2 2 Number ofinflection points where tilt 1 1 1 1 direction is folded Diffractionangle (532) [°] 32 32 32 32 Wavelength dependency of diffraction A A A Aefficiency

[Evaluation]

<Evaluation of Diffraction Efficiency>

In a case where light was incident into the prepared liquid crystaldiffraction element prepared in Comparative Example 1 and Examples 3, 4,and 8 while changing an incidence angle in a range of ±40° (at aninterval of 10°) from the front (direction with an angle of 0° withrespect to the normal line), the diffraction efficiency of emitted lightwas evaluated.

Specifically, each of laser light components having output centralwavelengths of 405 nm, 450 nm, 532 nm, and 650 nm was irradiated to beincident into the prepared liquid crystal diffraction element from alight source. In the emitted light from the liquid crystal diffractionelement, the intensities of diffracted light (first-order light)diffracted in a desired direction, zero-order light (emitted in the samedirection as incidence light) emitted in the other directions, andnegative first-order light (light diffracted in a −θ direction in a casewhere the diffraction angle of first-order light with respect tozero-order light was represented by θ) were measured using aphotodetector, and the diffraction efficiency at each of the wavelengthswas calculated from the following expression.

Diffraction Efficiency=First-Order Light/(First-Order Light+Zero-OrderLight+(Negative First-Order Light))

The average value of the diffraction efficiencies was obtained from themeasured values at the wavelengths of 405 nm, 450 nm, 532 nm, and 650 nmthat were measured at different incidence angles, and the wavelengthdependence of the diffraction efficiency was evaluated.

Laser light was caused to be vertically incident into the circularlypolarizing plate corresponding to the wavelength of the laser light tobe converted into circularly polarized light, the circularly polarizedlight was incident into the prepared liquid crystal diffraction element,and the evaluation was performed.

In addition, in the liquid crystal alignment pattern of the preparedliquid crystal diffraction element, the evaluation was performed atthree positions including the center portion of the concentric circleand the vicinity of the concentric circle (the single period was 10 μm),the vicinity of an end part (the single period was 1 μm), and the endpart (the single period was 0.6 μm).

As a result of the evaluation, as compared to Comparative Example 1, inall of the liquid crystal diffraction elements according to Examples 3,4, and 8, a high diffraction efficiency (average value) was obtained.

In addition, as a result of the evaluation, as compared to Example 3,the average value of the diffraction efficiencies in Example 4 wasimproved, and the average value of the diffraction efficiencies inExample 8 was further improved.

It can be seen from the above results that, as the difference Δn₅₅₀ inrefractive index of the liquid crystal layer of the liquid crystaldiffraction element increases, the light utilization efficiency withrespect to the different incidence angles is improved.

<Preparation of Circularly Polarizing Plate>

(Preparation of Retardation Plate)

A film including a cellulose acylate film, an alignment film, and anoptically-anisotropic layer C was obtained using the same method as apositive A plate described in paragraphs “0102” to “0126” ofJP2019-215416A.

The optically-anisotropic layer C was the positive A plate (retardationplate), and the thickness of the positive A plate was controlled suchthat Re(550) was 138 nm.

The prepared retardation plate was bonded to a linearly polarizing platethrough a pressure sensitive adhesive to prepare a circularly polarizingplate. The retardation plate and the linearly polarizing plate weredisposed such that a relative angle between a slow axis of theretardation plate and an absorption axis of the linearly polarizingplate was 45°.

<Preparation of Optical Element>

The prepared circularly polarizing plate was bonded to the liquidcrystal diffraction element prepared in each of Examples 1 to 8 toprepare an optical element. The optical element was formed by disposingthe liquid crystal diffraction element, the retardation plate, and thelinearly polarizing plate in this order.

[Evaluation]

In a case where light was incident into the prepared optical elementfrom the front (direction with an angle of 0° with respect to the normalline), the intensity of emitted light was evaluated.

Specifically, each of laser light components having output centralwavelengths of 405 nm, 450 nm, 532 nm, and 650 nm was irradiated to bevertically incident into the prepared optical element from a lightsource. In the emitted light from the liquid crystal diffractionelement, the intensities of diffracted light (first-order light)diffracted in a desired direction and zero-order light (emitted in thesame direction as incidence light) emitted in the other directions weremeasured using a photodetector. Laser light was caused to be verticallyincident into the circularly polarizing plate corresponding to thewavelength of the laser light to be converted into circularly polarizedlight, the circularly polarized light was incident from the liquidcrystal diffraction element side of the prepared optical element, andthe evaluation was performed.

It was verified that, in the optical element where the circularlypolarizing plate is bonded to each of the liquid crystal diffractionelements prepared in Examples 1 to 7, before bonding the circularlypolarizing plate, the intensity of zero-order light at any wavelengthcan be significantly reduced, and the contrast ratio (intensity ratiofirst-order light/zero-order light) can be improved. In Examples 5 to 7,the incident circularly polarized light and the arrangement of theretardation plate and the linearly polarizing plate in the circularlypolarizing plate were appropriately changed to perform the evaluation.In addition, in Example 7, in the vicinity of the end part (the singleperiod was 1 μm), the incidence angle of light into the liquid crystaldiffraction element was 25° to perform the evaluation.

[Evaluation]

<Evaluation of Incidence Angle Dependence>

In a case where light was incident into the optical element includingthe liquid crystal diffraction element prepared in Comparative Example 1and Examples 3, 4, and 8 while changing an incidence angle in a range of±40° (at an interval of 10°) from the front (direction with an angle of0° with respect to the normal line), the intensity of emitted light wasevaluated.

Specifically, each of laser light components having output centralwavelengths of 405 nm, 450 nm, 532 nm, and 650 nm was irradiated to beincident into the prepared liquid crystal diffraction element from alight source. In the emitted light from the liquid crystal diffractionelement, the intensities of diffracted light (first-order light)diffracted in a desired direction and zero-order light (emitted in thesame direction as incidence light) emitted in the other directions weremeasured using a photodetector.

The average value of the diffraction efficiencies with respect to theincidence angles was obtained from each of the measured values at thewavelengths of 405 nm, 450 nm, 532 nm, and 650 nm that were measured atdifferent incidence angles.

In addition, in the liquid crystal alignment pattern of the preparedliquid crystal diffraction element, the evaluation was performed atthree positions including the center portion of the concentric circleand the vicinity of the concentric circle (the single period was 10 μm),the vicinity of an end part (the single period was 1 μm), and the endpart (the single period was 0.6 μm).

Laser light was caused to be vertically incident into the circularlypolarizing plate corresponding to the wavelength of the laser light tobe converted into circularly polarized light, the circularly polarizedlight was incident from the liquid crystal diffraction element side ofthe prepared optical element, and the evaluation was performed.

It was verified that, in the optical element where the circularlypolarizing plate is bonded to each of the liquid crystal diffractionelements prepared in Examples 3, 4, and 8, before bonding the circularlypolarizing plate, the intensity of zero-order light at any wavelengthcan be significantly reduced, and the contrast ratio (intensity ratiofirst-order light/zero-order light) can be improved. In addition, ascompared to the optical element including the liquid crystal diffractionelement prepared in Comparative Example 1, in all of the opticalelements including the liquid crystal diffraction elements prepared inExamples 3, 4, and 8, a high contrast ratio was obtained.

In addition, as a result of the evaluation, as compared to the opticalelement including the liquid crystal diffraction element prepared inExample 3, the average value of the contrast ratios with respect to theincidence angles in the optical element including the liquid crystaldiffraction element prepared in Example 4 was improved, and the averagevalue of the contrast ratios with respect to the incidence angles in theoptical element including the liquid crystal diffraction elementprepared in Example 8 was further improved.

It can be seen from the above results that, even in the optical elementwhere the circularly polarizing plate is bonded to the liquid crystaldiffraction element, as the difference Δn₅₅₀ in refractive index of theliquid crystal layer increases, the contrast ratio with respect to thedifferent incidence angles is improved.

<Preparation of Circularly Polarizing Plate>

A circularly polarizing plate was prepared using the same method as thatof preparing the above-described circularly polarizing plate, exceptthat the linearly polarizing plate (polyvinyl alcohol layer type) waschanged to an absorptive polarizing plate prepared as described above.

<Preparation of Optical Element>

A circularly polarizing plate prepared using the absorptive polarizingplate prepared as described below was bonded to the liquid crystaldiffraction element prepared in each of Examples 1 to 8 to prepare anoptical element. The optical element was formed by disposing the liquidcrystal diffraction element, the retardation plate, and the linearlypolarizing plate in this order.

[Preparation of Absorptive Polarizer]

<Preparation of Transparent Support 1>

A coating liquid PA1 for forming an alignment layer described below wascontinuously applied to a cellulose acylate film (TAC substrate having athickness of 40 μm; TG 40, manufactured by Fujifilm Corporation) using awire bar. The support on which the coating film was formed was driedwith hot air at 140° C. for 120 seconds. Next, the coating film wasirradiated with polarized ultraviolet rays (10 mJ/cm², using anultra-high pressure mercury lamp) to form a photoalignment layer PA1. Asa result, a TAC film with the photoalignment layer was obtained.

The film thickness was 0.3 μm.

(Coating Liquid PA1 for Forming Alignment Layer) The following polymerPA-1  100.00 parts by mass The following acid generator PAG-1   5.00parts by mass The following acid generator CPI-110TF  0.005 parts bymass Xylene 1220.00 parts by mass Methyl isobutyl ketone  122.00 partsby mass Polymer PA-1

Acid Generator PAG-1

Acid Generator CPI-110TF

<Formation of Light-Absorption Anisotropic Layer P1>

A composition P1 for forming a light-absorption anisotropic layerdescribed below was continuously applied to the obtained alignment layerPA1 using a wire bar to form a coating layer P1.

Next, the coating layer P1 was heated at 140° C. for 30 seconds and wascooled to room temperature (23° C.).

Next, the coating layer P1 was heated at 90° C. for 60 seconds and wascooled to room temperature.

Next, the coating layer P1 was irradiated with light using a LED light(central wavelength: 365 nm) for 2 seconds under irradiation conditionsof an illuminance of 200 mW/cm² to form the light-absorption anisotropiclayer P1 on the alignment layer PA1.

The film thickness was 1.6 μm.

As a result, a laminate 1B was obtained.

Composition of Composition P1 for forming Light-Absorption AnisotropicLayer The following dichroic substance D-1  0.25 parts by mass Thefollowing dichroic substance D-2  0.36 parts by mass The followingdichroic substance D-3  0.59 parts by mass The following polymer liquidcrystal compound P-1  2.21 parts by mass The followinglow-molecular-weight liquid crystalline compound M-1  1.36 parts by massPolymerization Initiator IRGACURE OXE-02 (manufactured by BASF SE) 0.200parts by mass The following surfactant F-1 0.026 parts by massCyclopentanone 46.00 parts by mass Tetrahydrofuran 46.00 parts by massBenzyl alcohol  3.00 parts by mass D-1

D-2

D-3

Polymer Liquid Crystal Compound P-1

Low-Molecular-Weight Liquid Crystalline Compound M-1

Surfactant F-1

<Preparation of UV Adhesive>

The following UV adhesive composition was prepared.

UV Adhesive Composition CEL2021P (manufactured by Daicel Corporation)  70 parts by mass 1,4-butanediol diglycidyl ether   20 parts by mass2-ethylhexyl glycidyl ether   10 parts by mass CPI-100P 2.25 parts bymass CPI-100P

<Preparation of Absorptive Polarizing Film>

TECHNOLLOY S001G (methacrylic resin, thickness: 50 μm, tan δ peaktemperature: 128° C., manufactured by Sumika Acryl Co., Ltd.) as a resinsubstrate S1 was bonded to the surface of the light-absorptionanisotropic layer of the laminate 1B using the UV adhesive. Next, onlythe cellulose acylate film 1 was peeled off, and an absorptivepolarizing film in which the resin substrate, the adhesive layer, thelight-absorption anisotropic layer, and the alignment layer weredisposed in this order was prepared. The thickness of the UV adhesivelayer was 2 μm.

The arithmetic average roughness Ra of the obtained absorptivepolarizing film was 10 nm or less. On the other hand, the arithmeticaverage roughness Ra of the linearly polarizing plate (polyvinyl alcohollayer type) was 20 nm or more.

As a result, in the prepared absorptive polarizing film, the deflection(for example, refraction or scattering) of light from the surfaceunevenness of the polarizing film can be reduced. In addition, in a casewhere the image display apparatus is used, the distortion of an image tobe displayed can be suppressed.

The arithmetic average roughness Ra was measured using an interferometer“Vertscan” (manufactured by Mitsubishi Chemical Systems Inc.).

[Evaluation]

In a case where light was incident into the prepared optical elementfrom the front (direction with an angle of 0° with respect to the normalline), the intensity of emitted light was evaluated.

Specifically, laser light components having output central wavelengthsof 405 nm, 450 nm, 532 nm, and 650 nm were irradiated to be verticallyincident into the prepared optical element from a light source. In theemitted light from the liquid crystal diffraction element, theintensities of diffracted light (first-order light) diffracted in adesired direction and zero-order light (emitted in the same direction asincidence light) emitted in the other directions were measured using aphotodetector. Laser light was caused to be vertically incident into thecircularly polarizing plate corresponding to the wavelength of the laserlight to be converted into circularly polarized light, the circularlypolarized light was incident from the liquid crystal diffraction elementside of the prepared optical element, and the evaluation was performed.

It was verified that, in the optical element where the circularlypolarizing plate is bonded to each of the liquid crystal diffractionelements prepared in Examples 1 to 7, before bonding the circularlypolarizing plate, the intensity of zero-order light at any wavelengthcan be significantly reduced, and the contrast ratio (intensity ratiofirst-order light/zero-order light) can be improved. In Examples 5 to 7,the incident circularly polarized light and the arrangement of theretardation plate and the linearly polarizing plate in the circularlypolarizing plate were appropriately changed to perform the evaluation.In addition, in Example 7, in the vicinity of the end part (the singleperiod was 1 μm), the incidence angle of light into the liquid crystaldiffraction element was 25° to perform the evaluation.

[Evaluation]

<Evaluation of Incidence Angle Dependence>

In a case where light was incident into the optical element includingthe liquid crystal diffraction element prepared in Comparative Example 1and Examples 3, 4, and 8 while changing an incidence angle in a range of±40° (at an interval of 10°) from the front (direction with an angle of0° with respect to the normal line), the intensity of emitted light wasevaluated.

Specifically, each of laser light components having output centralwavelengths of 405 nm, 450 nm, 532 nm, and 650 nm was irradiated to beincident into the prepared liquid crystal diffraction element from alight source. In the emitted light from the liquid crystal diffractionelement, the intensities of diffracted light (first-order light)diffracted in a desired direction and zero-order light (emitted in thesame direction as incidence light) emitted in the other directions weremeasured using a photodetector.

The average value of the diffraction efficiencies with respect to theincidence angles was obtained from each of the measured values at thewavelengths of 405 nm, 450 nm, 532 nm, and 650 nm that were measured atdifferent incidence angles.

In addition, in the liquid crystal alignment pattern of the preparedliquid crystal diffraction element, the evaluation was performed atthree positions including the center portion of the concentric circleand the vicinity of the concentric circle (the single period was 10 μm),the vicinity of an end part (the single period was 1 μm), and the endpart (the single period was 0.6 μm).

Laser light was caused to be vertically incident into the circularlypolarizing plate corresponding to the wavelength of the laser light tobe converted into circularly polarized light, the circularly polarizedlight was incident from the liquid crystal diffraction element side ofthe prepared optical element, and the evaluation was performed.

It was verified that, in the optical element where the circularlypolarizing plate is bonded to each of the liquid crystal diffractionelements prepared in Examples 3, 4, and 8, before bonding the circularlypolarizing plate, the intensity of zero-order light at any wavelengthcan be significantly reduced, and the contrast ratio (intensity ratiofirst-order light/zero-order light) can be improved. In addition, ascompared to the optical element including the liquid crystal diffractionelement prepared in Comparative Example 1, in all of the opticalelements including the liquid crystal diffraction elements prepared inExamples 3, 4, and 8, a high contrast ratio was obtained.

In addition, as a result of the evaluation, as compared to the opticalelement including the liquid crystal diffraction element prepared inExample 3, the average value of the contrast ratios with respect to theincidence angles in the optical element including the liquid crystaldiffraction element prepared in Example 4 was improved, and the averagevalue of the contrast ratios with respect to the incidence angles in theoptical element including the liquid crystal diffraction elementprepared in Example 8 was further improved.

It can be seen from the above results that, even in the optical elementwhere the circularly polarizing plate is bonded to the liquid crystaldiffraction element, as the difference Δn₅₅₀ in refractive index of theliquid crystal layer increases, the contrast ratio with respect to thedifferent incidence angles is improved.

<Change of Support>

Using a method described below, the support of the liquid crystaldiffraction element can be appropriately changed depending on purposes.In addition, in the method described below, the thickness between theliquid crystal diffraction element and the changed support can bereduced, and the in-plane thickness of the liquid crystal diffractionelement after changing the support can be made uniform with respect to,for example, a pressure sensitive adhesive (thickness: severalmicrometers to several tens of micrometers). This way, even in a casewhere the support of the liquid crystal diffraction element was changed,by making the in-plane thickness uniform, a direction of light emittedfrom the liquid crystal diffraction element can be accurately controlledin a plane.

The liquid crystal diffraction element and the new support may belaminated, for example, in the following procedure.

(1) A temporary support is bonded to the liquid crystal layer side ofthe support, the alignment film, and the liquid crystal diffractionelement to be laminated. In this example, as the temporary support,MASTACK AS3-304 manufactured by Fujimori Kogyo Co., Ltd. was used.

(2) Next, the support and the alignment film present from the step ofpreparing the liquid crystal diffraction element are peeled off toexpose the interface of the liquid crystal diffraction element on thealignment film side.

(3) A silicon oxide layer (SiO_(X) layer) is formed on both of theinterface of the liquid crystal diffraction element on the alignmentfilm side and the interface of the newly prepared support. A method offorming the silicon oxide layer is not limited and, for example, vacuumdeposition is preferably used. In this example, the formation of thesilicon oxide layer was performed using a vapor deposition device (modelnumber: ULEYES) manufactured by ULVAC, Inc. As a vapor depositionsource, SiO₂ powder was used. The thickness of the silicon oxide layeris not limited and is preferably 50 nm or less. In this example, thethickness of the silicon oxide film was 50 nm or less.

(4) Next, plasma treatment is performed on both of the formed siliconoxide films, the formed silicon oxide layers are bonded to each other at120° C., and the temporary support is peeled off.

Through the steps (1) to (4), a diffraction element where the liquidcrystal diffraction element and the newly prepared support are laminatedcan be prepared. In addition, by changing the support to another liquidcrystal diffraction element and repeating the steps (1) to (4), adiffraction element where two or three or more liquid crystaldiffraction elements are laminated can be prepared.

Through the steps (1) to (4) the support of the liquid crystaldiffraction element prepared in Example 1 was changed to a glasssubstrate having a thickness of 0.3 mm. As a comparison, using apressure sensitive adhesive having a thickness of 25 μm, the support ofthe liquid crystal diffraction element prepared in Example 1 was changedto a glass substrate having a thickness of 0.3 mm (the liquid crystaldiffraction element was bonded to the glass substrate through thepressure sensitive adhesive). In the liquid crystal diffraction elementprepared through the steps (1) to (4), the in-plane thickness of theliquid crystal diffraction element was able to be made more uniform thanthat of the liquid crystal diffraction element prepared through thepressure sensitive adhesive.

<Preparation of Laminate>

Likewise, a laminate including the liquid crystal diffraction elementand another optical member or the like can be prepared.

For example, a laminate including a liquid crystal diffraction element,a retardation plate, and a polarizing plate was prepared using thefollowing method.

A silicon oxide layer (SiO_(x) layer) was formed on a liquid crystallayer side of a liquid crystal diffraction element including a support,an alignment film, and a liquid crystal layer to be laminated and on abonding surface side of a retardation plate to be bonded to the liquidcrystal diffraction element. A method of forming the silicon oxide layeris not limited and, for example, vacuum deposition is preferably used.In this example, the formation of the silicon oxide layer was performedusing a vapor deposition device (model number: ULEYES) manufactured byULVAC, Inc. As a vapor deposition source, SiO₂ powder was used. Thethickness of the silicon oxide layer is not limited and is preferably 50nm or less. In this example, the thickness of the silicon oxide film was50 nm or less. Plasma treatment was performed on both of the formedsilicon oxide films, and the formed silicon oxide layers were bonded toeach other at 120° C. As a result, the laminate including the liquidcrystal diffraction element and the retardation plate was formed.Likewise, by bonding a polarizing plate to the retardation plate andpeeling off the support and the alignment film, a laminate consisting ofthe liquid crystal layer (liquid crystal diffraction element), theretardation plate, and the polarizing plate was prepared.

As the liquid crystal diffraction element, the liquid crystaldiffraction element prepared in each of Examples 1 to 7 was used. As theretardation plate, the retardation plate used for preparing theabove-described circularly polarizing plate was used. As the polarizingplate, a laminate including each of the above-described linearlypolarizing plate (polyvinyl alcohol layer type) and the absorptivepolarizing plate was prepared.

It was verified that, in the optical element as the laminate includingthe liquid crystal diffraction element, the retardation plate, and thepolarizing plate, before bonding the circularly polarizing plate (thelaminate of the retardation plate and the polarizing plate), theintensity of zero-order light at any wavelength can be significantlyreduced, and the contrast ratio (intensity ratio first-orderlight/zero-order light) can be improved.

As can be seen from the above results, the effects of the presentinvention are obvious.

EXPLANATION OF REFERENCES

-   -   10 a, 10 b: liquid crystal diffraction element    -   30: support    -   32: alignment film    -   36 a, 36 b: optically-anisotropic layer    -   37 a to 37 g: region    -   40: liquid crystal compound    -   40A: optical axis    -   42: bright portion    -   44: dark portion    -   60, 80: exposure device    -   62, 82: laser    -   64, 84: light source    -   65: λ/2 plate    -   68: beam splitter    -   70A, 70B, 90A, 90B: mirror    -   72A, 72B, 96: λ/4 plate    -   86, 94: polarization beam splitter    -   92: lens    -   Λ, Λ₁, Λ₂: single period    -   D, A₁ to A₃: arrangement axis    -   R: region    -   M: laser light    -   MA, MB: beam    -   MP: P polarized light    -   MS: S polarized light    -   P₀: linearly polarized light    -   P_(R): right circularly polarized light    -   P_(L): left circularly polarized light    -   α: intersecting angle    -   L₁, L₂, L₃ to L₁₅: light

What is claimed is:
 1. A liquid crystal diffraction element comprising:an optically-anisotropic layer that is formed of a liquid crystalcomposition including a liquid crystal compound, wherein theoptically-anisotropic layer has a liquid crystal alignment pattern inwhich a direction of an optical axis derived from the liquid crystalcompound changes while continuously rotating in at least one in-planedirection, in a case where a length over which the direction of theoptical axis derived from the liquid crystal compound rotates by 180° ina plane is set as a single period, a length of the single period in theliquid crystal alignment pattern gradually changes in the one in-planedirection, in a cross-sectional image of the optically-anisotropic layerobtained by observing a cross-section taken in a thickness directionparallel to the one in-plane direction with a scanning electronmicroscope, the optically-anisotropic layer has bright portions and darkportions extending from one surface to another surface and each of thedark portions has two or more inflection points of angle, theoptically-anisotropic layer has regions where tilt directions of thedark portions are different from each other in the thickness direction,and an average tilt angle of the dark portion gradually changes in theone in-plane direction.
 2. The liquid crystal diffraction elementpattern according to claim 1, wherein as the length of the single periodin the liquid crystal alignment pattern decreases, the average tiltangle of the dark portion increases.
 3. The liquid crystal diffractionelement according to claim 1, wherein the number of inflection pointswhere the tilt direction of the dark portion is folded is an odd number.4. The liquid crystal diffraction element according to claim 1, whereinthe number of inflection points where the tilt direction of the darkportion is folded is one.
 5. The liquid crystal diffraction elementaccording to claim 1, wherein the number of inflection points where thetilt direction of the dark portion is folded is three.
 6. The liquidcrystal diffraction element according to claim 1, wherein the liquidcrystal alignment pattern of the optically-anisotropic layer is aconcentric circular pattern having a concentric circular shape where theone in-plane direction in which the direction of the optical axisderived from the liquid crystal compound changes while continuouslyrotating moves from an inner side toward an outer side.
 7. The liquidcrystal diffraction element according to claim 6, wherein in theoptically-anisotropic layer, shapes of the bright portions and the darkportions in a cross-section of a center portion of the concentriccircular shape are symmetrical with respect to a center line of theoptically-anisotropic layer in the thickness direction, and shapes ofthe bright portions and the dark portions in a cross-section of an endpart of the concentric circular shape are asymmetrical with respect tothe center line of the optically-anisotropic layer in the thicknessdirection.
 8. The liquid crystal diffraction element according to claim6, wherein in the optically-anisotropic layer, shapes of the brightportions and the dark portions in a cross-section of a center portion ofthe concentric circular shape are asymmetrical with respect to a centerline of the optically-anisotropic layer in the thickness direction, andshapes of the bright portions and the dark portions in a cross-sectionof an end part of the concentric circular shape are asymmetrical withrespect to the center line of the optically-anisotropic layer in thethickness direction.
 9. The liquid crystal diffraction element accordingto claim 1, wherein a difference Δn₅₅₀ in refractive index generated byrefractive index anisotropy of the optically-anisotropic layer is 0.2 ormore.
 10. The liquid crystal diffraction element according to claim 1,wherein a region where the length of the single period in the liquidcrystal alignment pattern is 1.0 μm or less is provided in a plane. 11.An optical element comprising: the liquid crystal diffraction elementaccording to claim 1; and a circularly polarizing plate.
 12. The opticalelement according to claim 11, wherein the circularly polarizing plateconsists of a retardation plate and a polarizer, and the liquid crystaldiffraction element, the retardation plate, and the polarizer aredisposed in this order.
 13. The optical element according to claim 12,wherein the retardation plate is a λ/4 plate.
 14. The optical elementaccording to claim 12, wherein the retardation plate has reversewavelength dispersibility.
 15. An optical element comprising, in thefollowing order: the liquid crystal diffraction element according toclaim 1; a silicon oxide layer; and a support.
 16. An optical elementcomprising: at least one liquid crystal diffraction element according toclaim 1; and at least one phase modulation element.
 17. An image displayunit comprising: the liquid crystal diffraction element according toclaim
 1. 18. A head-mounted display comprising: the image display unitaccording to claim
 17. 19. A beam steering comprising: the liquidcrystal diffraction element according to claim
 1. 20. A sensorcomprising: the liquid crystal diffraction element according to claim 1.